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![Paul E. McKenney](/assets/img/avatar_default.png)
The rt_mutex structure's ->owner field is read locklessly, so this commit adds the WRITE_ONCE() to an update in order to provide proper documentation and READ_ONCE()/WRITE_ONCE() pairing. This data race was reported by KCSAN. Not appropriate for backporting due to failure being unlikely. Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Will Deacon <will@kernel.org>
1923 lines
51 KiB
C
1923 lines
51 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* RT-Mutexes: simple blocking mutual exclusion locks with PI support
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*
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* started by Ingo Molnar and Thomas Gleixner.
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*
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* Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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* Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
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* Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
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* Copyright (C) 2006 Esben Nielsen
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*
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* See Documentation/locking/rt-mutex-design.rst for details.
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*/
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#include <linux/spinlock.h>
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#include <linux/export.h>
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#include <linux/sched/signal.h>
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#include <linux/sched/rt.h>
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#include <linux/sched/deadline.h>
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#include <linux/sched/wake_q.h>
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#include <linux/sched/debug.h>
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#include <linux/timer.h>
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#include "rtmutex_common.h"
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/*
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* lock->owner state tracking:
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*
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* lock->owner holds the task_struct pointer of the owner. Bit 0
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* is used to keep track of the "lock has waiters" state.
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*
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* owner bit0
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* NULL 0 lock is free (fast acquire possible)
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* NULL 1 lock is free and has waiters and the top waiter
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* is going to take the lock*
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* taskpointer 0 lock is held (fast release possible)
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* taskpointer 1 lock is held and has waiters**
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*
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* The fast atomic compare exchange based acquire and release is only
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* possible when bit 0 of lock->owner is 0.
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*
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* (*) It also can be a transitional state when grabbing the lock
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* with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
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* we need to set the bit0 before looking at the lock, and the owner may be
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* NULL in this small time, hence this can be a transitional state.
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*
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* (**) There is a small time when bit 0 is set but there are no
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* waiters. This can happen when grabbing the lock in the slow path.
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* To prevent a cmpxchg of the owner releasing the lock, we need to
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* set this bit before looking at the lock.
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*/
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static void
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rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
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{
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unsigned long val = (unsigned long)owner;
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if (rt_mutex_has_waiters(lock))
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val |= RT_MUTEX_HAS_WAITERS;
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WRITE_ONCE(lock->owner, (struct task_struct *)val);
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}
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static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
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{
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lock->owner = (struct task_struct *)
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((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
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}
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static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
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{
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unsigned long owner, *p = (unsigned long *) &lock->owner;
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if (rt_mutex_has_waiters(lock))
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return;
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/*
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* The rbtree has no waiters enqueued, now make sure that the
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* lock->owner still has the waiters bit set, otherwise the
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* following can happen:
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*
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* CPU 0 CPU 1 CPU2
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* l->owner=T1
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* rt_mutex_lock(l)
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* lock(l->lock)
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* l->owner = T1 | HAS_WAITERS;
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* enqueue(T2)
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* boost()
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* unlock(l->lock)
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* block()
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*
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* rt_mutex_lock(l)
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* lock(l->lock)
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* l->owner = T1 | HAS_WAITERS;
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* enqueue(T3)
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* boost()
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* unlock(l->lock)
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* block()
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* signal(->T2) signal(->T3)
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* lock(l->lock)
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* dequeue(T2)
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* deboost()
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* unlock(l->lock)
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* lock(l->lock)
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* dequeue(T3)
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* ==> wait list is empty
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* deboost()
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* unlock(l->lock)
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* lock(l->lock)
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* fixup_rt_mutex_waiters()
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* if (wait_list_empty(l) {
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* l->owner = owner
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* owner = l->owner & ~HAS_WAITERS;
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* ==> l->owner = T1
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* }
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* lock(l->lock)
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* rt_mutex_unlock(l) fixup_rt_mutex_waiters()
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* if (wait_list_empty(l) {
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* owner = l->owner & ~HAS_WAITERS;
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* cmpxchg(l->owner, T1, NULL)
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* ===> Success (l->owner = NULL)
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*
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* l->owner = owner
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* ==> l->owner = T1
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* }
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*
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* With the check for the waiter bit in place T3 on CPU2 will not
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* overwrite. All tasks fiddling with the waiters bit are
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* serialized by l->lock, so nothing else can modify the waiters
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* bit. If the bit is set then nothing can change l->owner either
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* so the simple RMW is safe. The cmpxchg() will simply fail if it
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* happens in the middle of the RMW because the waiters bit is
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* still set.
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*/
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owner = READ_ONCE(*p);
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if (owner & RT_MUTEX_HAS_WAITERS)
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WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
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}
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/*
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* We can speed up the acquire/release, if there's no debugging state to be
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* set up.
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*/
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#ifndef CONFIG_DEBUG_RT_MUTEXES
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# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
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# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
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# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
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/*
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* Callers must hold the ->wait_lock -- which is the whole purpose as we force
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* all future threads that attempt to [Rmw] the lock to the slowpath. As such
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* relaxed semantics suffice.
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*/
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static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
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{
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unsigned long owner, *p = (unsigned long *) &lock->owner;
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do {
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owner = *p;
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} while (cmpxchg_relaxed(p, owner,
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owner | RT_MUTEX_HAS_WAITERS) != owner);
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}
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/*
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* Safe fastpath aware unlock:
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* 1) Clear the waiters bit
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* 2) Drop lock->wait_lock
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* 3) Try to unlock the lock with cmpxchg
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*/
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static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
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unsigned long flags)
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__releases(lock->wait_lock)
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{
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struct task_struct *owner = rt_mutex_owner(lock);
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clear_rt_mutex_waiters(lock);
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raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
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/*
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* If a new waiter comes in between the unlock and the cmpxchg
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* we have two situations:
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*
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* unlock(wait_lock);
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* lock(wait_lock);
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* cmpxchg(p, owner, 0) == owner
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* mark_rt_mutex_waiters(lock);
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* acquire(lock);
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* or:
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*
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* unlock(wait_lock);
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* lock(wait_lock);
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* mark_rt_mutex_waiters(lock);
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*
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* cmpxchg(p, owner, 0) != owner
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* enqueue_waiter();
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* unlock(wait_lock);
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* lock(wait_lock);
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* wake waiter();
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* unlock(wait_lock);
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* lock(wait_lock);
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* acquire(lock);
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*/
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return rt_mutex_cmpxchg_release(lock, owner, NULL);
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}
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#else
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# define rt_mutex_cmpxchg_relaxed(l,c,n) (0)
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# define rt_mutex_cmpxchg_acquire(l,c,n) (0)
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# define rt_mutex_cmpxchg_release(l,c,n) (0)
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static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
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{
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lock->owner = (struct task_struct *)
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((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
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}
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/*
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* Simple slow path only version: lock->owner is protected by lock->wait_lock.
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*/
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static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
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unsigned long flags)
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__releases(lock->wait_lock)
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{
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lock->owner = NULL;
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raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
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return true;
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}
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#endif
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/*
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* Only use with rt_mutex_waiter_{less,equal}()
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*/
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#define task_to_waiter(p) \
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&(struct rt_mutex_waiter){ .prio = (p)->prio, .deadline = (p)->dl.deadline }
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static inline int
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rt_mutex_waiter_less(struct rt_mutex_waiter *left,
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struct rt_mutex_waiter *right)
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{
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if (left->prio < right->prio)
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return 1;
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/*
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* If both waiters have dl_prio(), we check the deadlines of the
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* associated tasks.
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* If left waiter has a dl_prio(), and we didn't return 1 above,
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* then right waiter has a dl_prio() too.
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*/
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if (dl_prio(left->prio))
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return dl_time_before(left->deadline, right->deadline);
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return 0;
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}
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static inline int
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rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
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struct rt_mutex_waiter *right)
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{
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if (left->prio != right->prio)
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return 0;
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/*
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* If both waiters have dl_prio(), we check the deadlines of the
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* associated tasks.
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* If left waiter has a dl_prio(), and we didn't return 0 above,
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* then right waiter has a dl_prio() too.
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*/
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if (dl_prio(left->prio))
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return left->deadline == right->deadline;
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return 1;
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}
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static void
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rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
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{
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struct rb_node **link = &lock->waiters.rb_root.rb_node;
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struct rb_node *parent = NULL;
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struct rt_mutex_waiter *entry;
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bool leftmost = true;
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while (*link) {
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parent = *link;
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entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
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if (rt_mutex_waiter_less(waiter, entry)) {
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link = &parent->rb_left;
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} else {
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link = &parent->rb_right;
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leftmost = false;
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}
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}
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rb_link_node(&waiter->tree_entry, parent, link);
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rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);
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}
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static void
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rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
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{
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if (RB_EMPTY_NODE(&waiter->tree_entry))
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return;
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rb_erase_cached(&waiter->tree_entry, &lock->waiters);
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RB_CLEAR_NODE(&waiter->tree_entry);
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}
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static void
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rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
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{
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struct rb_node **link = &task->pi_waiters.rb_root.rb_node;
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struct rb_node *parent = NULL;
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struct rt_mutex_waiter *entry;
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bool leftmost = true;
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while (*link) {
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parent = *link;
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entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
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if (rt_mutex_waiter_less(waiter, entry)) {
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link = &parent->rb_left;
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} else {
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link = &parent->rb_right;
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leftmost = false;
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}
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}
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rb_link_node(&waiter->pi_tree_entry, parent, link);
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rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);
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}
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static void
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rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
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{
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if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
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return;
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rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
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RB_CLEAR_NODE(&waiter->pi_tree_entry);
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}
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static void rt_mutex_adjust_prio(struct task_struct *p)
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{
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struct task_struct *pi_task = NULL;
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lockdep_assert_held(&p->pi_lock);
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if (task_has_pi_waiters(p))
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pi_task = task_top_pi_waiter(p)->task;
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rt_mutex_setprio(p, pi_task);
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}
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/*
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* Deadlock detection is conditional:
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*
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* If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
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* if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
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*
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* If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
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* conducted independent of the detect argument.
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*
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* If the waiter argument is NULL this indicates the deboost path and
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* deadlock detection is disabled independent of the detect argument
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* and the config settings.
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*/
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static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
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enum rtmutex_chainwalk chwalk)
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{
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/*
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* This is just a wrapper function for the following call,
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* because debug_rt_mutex_detect_deadlock() smells like a magic
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* debug feature and I wanted to keep the cond function in the
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* main source file along with the comments instead of having
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* two of the same in the headers.
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*/
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return debug_rt_mutex_detect_deadlock(waiter, chwalk);
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}
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/*
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* Max number of times we'll walk the boosting chain:
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*/
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int max_lock_depth = 1024;
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static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
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{
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return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
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}
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/*
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* Adjust the priority chain. Also used for deadlock detection.
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* Decreases task's usage by one - may thus free the task.
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*
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* @task: the task owning the mutex (owner) for which a chain walk is
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* probably needed
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* @chwalk: do we have to carry out deadlock detection?
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* @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
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* things for a task that has just got its priority adjusted, and
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* is waiting on a mutex)
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* @next_lock: the mutex on which the owner of @orig_lock was blocked before
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* we dropped its pi_lock. Is never dereferenced, only used for
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* comparison to detect lock chain changes.
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* @orig_waiter: rt_mutex_waiter struct for the task that has just donated
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* its priority to the mutex owner (can be NULL in the case
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* depicted above or if the top waiter is gone away and we are
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* actually deboosting the owner)
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* @top_task: the current top waiter
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*
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* Returns 0 or -EDEADLK.
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*
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* Chain walk basics and protection scope
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*
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* [R] refcount on task
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* [P] task->pi_lock held
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* [L] rtmutex->wait_lock held
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*
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* Step Description Protected by
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* function arguments:
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* @task [R]
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* @orig_lock if != NULL @top_task is blocked on it
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* @next_lock Unprotected. Cannot be
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* dereferenced. Only used for
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* comparison.
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* @orig_waiter if != NULL @top_task is blocked on it
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* @top_task current, or in case of proxy
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* locking protected by calling
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* code
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* again:
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* loop_sanity_check();
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* retry:
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* [1] lock(task->pi_lock); [R] acquire [P]
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* [2] waiter = task->pi_blocked_on; [P]
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* [3] check_exit_conditions_1(); [P]
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* [4] lock = waiter->lock; [P]
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* [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
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* unlock(task->pi_lock); release [P]
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* goto retry;
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* }
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* [6] check_exit_conditions_2(); [P] + [L]
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* [7] requeue_lock_waiter(lock, waiter); [P] + [L]
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* [8] unlock(task->pi_lock); release [P]
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* put_task_struct(task); release [R]
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* [9] check_exit_conditions_3(); [L]
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* [10] task = owner(lock); [L]
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* get_task_struct(task); [L] acquire [R]
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* lock(task->pi_lock); [L] acquire [P]
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* [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
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* [12] check_exit_conditions_4(); [P] + [L]
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* [13] unlock(task->pi_lock); release [P]
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* unlock(lock->wait_lock); release [L]
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* goto again;
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*/
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static int rt_mutex_adjust_prio_chain(struct task_struct *task,
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enum rtmutex_chainwalk chwalk,
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struct rt_mutex *orig_lock,
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struct rt_mutex *next_lock,
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struct rt_mutex_waiter *orig_waiter,
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struct task_struct *top_task)
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{
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struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
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struct rt_mutex_waiter *prerequeue_top_waiter;
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int ret = 0, depth = 0;
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struct rt_mutex *lock;
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bool detect_deadlock;
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bool requeue = true;
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detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
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/*
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* The (de)boosting is a step by step approach with a lot of
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* pitfalls. We want this to be preemptible and we want hold a
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* maximum of two locks per step. So we have to check
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* carefully whether things change under us.
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*/
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again:
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/*
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* We limit the lock chain length for each invocation.
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*/
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if (++depth > max_lock_depth) {
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static int prev_max;
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|
|
|
/*
|
|
* Print this only once. If the admin changes the limit,
|
|
* print a new message when reaching the limit again.
|
|
*/
|
|
if (prev_max != max_lock_depth) {
|
|
prev_max = max_lock_depth;
|
|
printk(KERN_WARNING "Maximum lock depth %d reached "
|
|
"task: %s (%d)\n", max_lock_depth,
|
|
top_task->comm, task_pid_nr(top_task));
|
|
}
|
|
put_task_struct(task);
|
|
|
|
return -EDEADLK;
|
|
}
|
|
|
|
/*
|
|
* We are fully preemptible here and only hold the refcount on
|
|
* @task. So everything can have changed under us since the
|
|
* caller or our own code below (goto retry/again) dropped all
|
|
* locks.
|
|
*/
|
|
retry:
|
|
/*
|
|
* [1] Task cannot go away as we did a get_task() before !
|
|
*/
|
|
raw_spin_lock_irq(&task->pi_lock);
|
|
|
|
/*
|
|
* [2] Get the waiter on which @task is blocked on.
|
|
*/
|
|
waiter = task->pi_blocked_on;
|
|
|
|
/*
|
|
* [3] check_exit_conditions_1() protected by task->pi_lock.
|
|
*/
|
|
|
|
/*
|
|
* Check whether the end of the boosting chain has been
|
|
* reached or the state of the chain has changed while we
|
|
* dropped the locks.
|
|
*/
|
|
if (!waiter)
|
|
goto out_unlock_pi;
|
|
|
|
/*
|
|
* Check the orig_waiter state. After we dropped the locks,
|
|
* the previous owner of the lock might have released the lock.
|
|
*/
|
|
if (orig_waiter && !rt_mutex_owner(orig_lock))
|
|
goto out_unlock_pi;
|
|
|
|
/*
|
|
* We dropped all locks after taking a refcount on @task, so
|
|
* the task might have moved on in the lock chain or even left
|
|
* the chain completely and blocks now on an unrelated lock or
|
|
* on @orig_lock.
|
|
*
|
|
* We stored the lock on which @task was blocked in @next_lock,
|
|
* so we can detect the chain change.
|
|
*/
|
|
if (next_lock != waiter->lock)
|
|
goto out_unlock_pi;
|
|
|
|
/*
|
|
* Drop out, when the task has no waiters. Note,
|
|
* top_waiter can be NULL, when we are in the deboosting
|
|
* mode!
|
|
*/
|
|
if (top_waiter) {
|
|
if (!task_has_pi_waiters(task))
|
|
goto out_unlock_pi;
|
|
/*
|
|
* If deadlock detection is off, we stop here if we
|
|
* are not the top pi waiter of the task. If deadlock
|
|
* detection is enabled we continue, but stop the
|
|
* requeueing in the chain walk.
|
|
*/
|
|
if (top_waiter != task_top_pi_waiter(task)) {
|
|
if (!detect_deadlock)
|
|
goto out_unlock_pi;
|
|
else
|
|
requeue = false;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If the waiter priority is the same as the task priority
|
|
* then there is no further priority adjustment necessary. If
|
|
* deadlock detection is off, we stop the chain walk. If its
|
|
* enabled we continue, but stop the requeueing in the chain
|
|
* walk.
|
|
*/
|
|
if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
|
|
if (!detect_deadlock)
|
|
goto out_unlock_pi;
|
|
else
|
|
requeue = false;
|
|
}
|
|
|
|
/*
|
|
* [4] Get the next lock
|
|
*/
|
|
lock = waiter->lock;
|
|
/*
|
|
* [5] We need to trylock here as we are holding task->pi_lock,
|
|
* which is the reverse lock order versus the other rtmutex
|
|
* operations.
|
|
*/
|
|
if (!raw_spin_trylock(&lock->wait_lock)) {
|
|
raw_spin_unlock_irq(&task->pi_lock);
|
|
cpu_relax();
|
|
goto retry;
|
|
}
|
|
|
|
/*
|
|
* [6] check_exit_conditions_2() protected by task->pi_lock and
|
|
* lock->wait_lock.
|
|
*
|
|
* Deadlock detection. If the lock is the same as the original
|
|
* lock which caused us to walk the lock chain or if the
|
|
* current lock is owned by the task which initiated the chain
|
|
* walk, we detected a deadlock.
|
|
*/
|
|
if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
|
|
debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
|
|
raw_spin_unlock(&lock->wait_lock);
|
|
ret = -EDEADLK;
|
|
goto out_unlock_pi;
|
|
}
|
|
|
|
/*
|
|
* If we just follow the lock chain for deadlock detection, no
|
|
* need to do all the requeue operations. To avoid a truckload
|
|
* of conditionals around the various places below, just do the
|
|
* minimum chain walk checks.
|
|
*/
|
|
if (!requeue) {
|
|
/*
|
|
* No requeue[7] here. Just release @task [8]
|
|
*/
|
|
raw_spin_unlock(&task->pi_lock);
|
|
put_task_struct(task);
|
|
|
|
/*
|
|
* [9] check_exit_conditions_3 protected by lock->wait_lock.
|
|
* If there is no owner of the lock, end of chain.
|
|
*/
|
|
if (!rt_mutex_owner(lock)) {
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
return 0;
|
|
}
|
|
|
|
/* [10] Grab the next task, i.e. owner of @lock */
|
|
task = get_task_struct(rt_mutex_owner(lock));
|
|
raw_spin_lock(&task->pi_lock);
|
|
|
|
/*
|
|
* No requeue [11] here. We just do deadlock detection.
|
|
*
|
|
* [12] Store whether owner is blocked
|
|
* itself. Decision is made after dropping the locks
|
|
*/
|
|
next_lock = task_blocked_on_lock(task);
|
|
/*
|
|
* Get the top waiter for the next iteration
|
|
*/
|
|
top_waiter = rt_mutex_top_waiter(lock);
|
|
|
|
/* [13] Drop locks */
|
|
raw_spin_unlock(&task->pi_lock);
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
|
|
/* If owner is not blocked, end of chain. */
|
|
if (!next_lock)
|
|
goto out_put_task;
|
|
goto again;
|
|
}
|
|
|
|
/*
|
|
* Store the current top waiter before doing the requeue
|
|
* operation on @lock. We need it for the boost/deboost
|
|
* decision below.
|
|
*/
|
|
prerequeue_top_waiter = rt_mutex_top_waiter(lock);
|
|
|
|
/* [7] Requeue the waiter in the lock waiter tree. */
|
|
rt_mutex_dequeue(lock, waiter);
|
|
|
|
/*
|
|
* Update the waiter prio fields now that we're dequeued.
|
|
*
|
|
* These values can have changed through either:
|
|
*
|
|
* sys_sched_set_scheduler() / sys_sched_setattr()
|
|
*
|
|
* or
|
|
*
|
|
* DL CBS enforcement advancing the effective deadline.
|
|
*
|
|
* Even though pi_waiters also uses these fields, and that tree is only
|
|
* updated in [11], we can do this here, since we hold [L], which
|
|
* serializes all pi_waiters access and rb_erase() does not care about
|
|
* the values of the node being removed.
|
|
*/
|
|
waiter->prio = task->prio;
|
|
waiter->deadline = task->dl.deadline;
|
|
|
|
rt_mutex_enqueue(lock, waiter);
|
|
|
|
/* [8] Release the task */
|
|
raw_spin_unlock(&task->pi_lock);
|
|
put_task_struct(task);
|
|
|
|
/*
|
|
* [9] check_exit_conditions_3 protected by lock->wait_lock.
|
|
*
|
|
* We must abort the chain walk if there is no lock owner even
|
|
* in the dead lock detection case, as we have nothing to
|
|
* follow here. This is the end of the chain we are walking.
|
|
*/
|
|
if (!rt_mutex_owner(lock)) {
|
|
/*
|
|
* If the requeue [7] above changed the top waiter,
|
|
* then we need to wake the new top waiter up to try
|
|
* to get the lock.
|
|
*/
|
|
if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
|
|
wake_up_process(rt_mutex_top_waiter(lock)->task);
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
return 0;
|
|
}
|
|
|
|
/* [10] Grab the next task, i.e. the owner of @lock */
|
|
task = get_task_struct(rt_mutex_owner(lock));
|
|
raw_spin_lock(&task->pi_lock);
|
|
|
|
/* [11] requeue the pi waiters if necessary */
|
|
if (waiter == rt_mutex_top_waiter(lock)) {
|
|
/*
|
|
* The waiter became the new top (highest priority)
|
|
* waiter on the lock. Replace the previous top waiter
|
|
* in the owner tasks pi waiters tree with this waiter
|
|
* and adjust the priority of the owner.
|
|
*/
|
|
rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
|
|
rt_mutex_enqueue_pi(task, waiter);
|
|
rt_mutex_adjust_prio(task);
|
|
|
|
} else if (prerequeue_top_waiter == waiter) {
|
|
/*
|
|
* The waiter was the top waiter on the lock, but is
|
|
* no longer the top prority waiter. Replace waiter in
|
|
* the owner tasks pi waiters tree with the new top
|
|
* (highest priority) waiter and adjust the priority
|
|
* of the owner.
|
|
* The new top waiter is stored in @waiter so that
|
|
* @waiter == @top_waiter evaluates to true below and
|
|
* we continue to deboost the rest of the chain.
|
|
*/
|
|
rt_mutex_dequeue_pi(task, waiter);
|
|
waiter = rt_mutex_top_waiter(lock);
|
|
rt_mutex_enqueue_pi(task, waiter);
|
|
rt_mutex_adjust_prio(task);
|
|
} else {
|
|
/*
|
|
* Nothing changed. No need to do any priority
|
|
* adjustment.
|
|
*/
|
|
}
|
|
|
|
/*
|
|
* [12] check_exit_conditions_4() protected by task->pi_lock
|
|
* and lock->wait_lock. The actual decisions are made after we
|
|
* dropped the locks.
|
|
*
|
|
* Check whether the task which owns the current lock is pi
|
|
* blocked itself. If yes we store a pointer to the lock for
|
|
* the lock chain change detection above. After we dropped
|
|
* task->pi_lock next_lock cannot be dereferenced anymore.
|
|
*/
|
|
next_lock = task_blocked_on_lock(task);
|
|
/*
|
|
* Store the top waiter of @lock for the end of chain walk
|
|
* decision below.
|
|
*/
|
|
top_waiter = rt_mutex_top_waiter(lock);
|
|
|
|
/* [13] Drop the locks */
|
|
raw_spin_unlock(&task->pi_lock);
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
|
|
/*
|
|
* Make the actual exit decisions [12], based on the stored
|
|
* values.
|
|
*
|
|
* We reached the end of the lock chain. Stop right here. No
|
|
* point to go back just to figure that out.
|
|
*/
|
|
if (!next_lock)
|
|
goto out_put_task;
|
|
|
|
/*
|
|
* If the current waiter is not the top waiter on the lock,
|
|
* then we can stop the chain walk here if we are not in full
|
|
* deadlock detection mode.
|
|
*/
|
|
if (!detect_deadlock && waiter != top_waiter)
|
|
goto out_put_task;
|
|
|
|
goto again;
|
|
|
|
out_unlock_pi:
|
|
raw_spin_unlock_irq(&task->pi_lock);
|
|
out_put_task:
|
|
put_task_struct(task);
|
|
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Try to take an rt-mutex
|
|
*
|
|
* Must be called with lock->wait_lock held and interrupts disabled
|
|
*
|
|
* @lock: The lock to be acquired.
|
|
* @task: The task which wants to acquire the lock
|
|
* @waiter: The waiter that is queued to the lock's wait tree if the
|
|
* callsite called task_blocked_on_lock(), otherwise NULL
|
|
*/
|
|
static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
|
|
struct rt_mutex_waiter *waiter)
|
|
{
|
|
lockdep_assert_held(&lock->wait_lock);
|
|
|
|
/*
|
|
* Before testing whether we can acquire @lock, we set the
|
|
* RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
|
|
* other tasks which try to modify @lock into the slow path
|
|
* and they serialize on @lock->wait_lock.
|
|
*
|
|
* The RT_MUTEX_HAS_WAITERS bit can have a transitional state
|
|
* as explained at the top of this file if and only if:
|
|
*
|
|
* - There is a lock owner. The caller must fixup the
|
|
* transient state if it does a trylock or leaves the lock
|
|
* function due to a signal or timeout.
|
|
*
|
|
* - @task acquires the lock and there are no other
|
|
* waiters. This is undone in rt_mutex_set_owner(@task) at
|
|
* the end of this function.
|
|
*/
|
|
mark_rt_mutex_waiters(lock);
|
|
|
|
/*
|
|
* If @lock has an owner, give up.
|
|
*/
|
|
if (rt_mutex_owner(lock))
|
|
return 0;
|
|
|
|
/*
|
|
* If @waiter != NULL, @task has already enqueued the waiter
|
|
* into @lock waiter tree. If @waiter == NULL then this is a
|
|
* trylock attempt.
|
|
*/
|
|
if (waiter) {
|
|
/*
|
|
* If waiter is not the highest priority waiter of
|
|
* @lock, give up.
|
|
*/
|
|
if (waiter != rt_mutex_top_waiter(lock))
|
|
return 0;
|
|
|
|
/*
|
|
* We can acquire the lock. Remove the waiter from the
|
|
* lock waiters tree.
|
|
*/
|
|
rt_mutex_dequeue(lock, waiter);
|
|
|
|
} else {
|
|
/*
|
|
* If the lock has waiters already we check whether @task is
|
|
* eligible to take over the lock.
|
|
*
|
|
* If there are no other waiters, @task can acquire
|
|
* the lock. @task->pi_blocked_on is NULL, so it does
|
|
* not need to be dequeued.
|
|
*/
|
|
if (rt_mutex_has_waiters(lock)) {
|
|
/*
|
|
* If @task->prio is greater than or equal to
|
|
* the top waiter priority (kernel view),
|
|
* @task lost.
|
|
*/
|
|
if (!rt_mutex_waiter_less(task_to_waiter(task),
|
|
rt_mutex_top_waiter(lock)))
|
|
return 0;
|
|
|
|
/*
|
|
* The current top waiter stays enqueued. We
|
|
* don't have to change anything in the lock
|
|
* waiters order.
|
|
*/
|
|
} else {
|
|
/*
|
|
* No waiters. Take the lock without the
|
|
* pi_lock dance.@task->pi_blocked_on is NULL
|
|
* and we have no waiters to enqueue in @task
|
|
* pi waiters tree.
|
|
*/
|
|
goto takeit;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Clear @task->pi_blocked_on. Requires protection by
|
|
* @task->pi_lock. Redundant operation for the @waiter == NULL
|
|
* case, but conditionals are more expensive than a redundant
|
|
* store.
|
|
*/
|
|
raw_spin_lock(&task->pi_lock);
|
|
task->pi_blocked_on = NULL;
|
|
/*
|
|
* Finish the lock acquisition. @task is the new owner. If
|
|
* other waiters exist we have to insert the highest priority
|
|
* waiter into @task->pi_waiters tree.
|
|
*/
|
|
if (rt_mutex_has_waiters(lock))
|
|
rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
|
|
raw_spin_unlock(&task->pi_lock);
|
|
|
|
takeit:
|
|
/* We got the lock. */
|
|
debug_rt_mutex_lock(lock);
|
|
|
|
/*
|
|
* This either preserves the RT_MUTEX_HAS_WAITERS bit if there
|
|
* are still waiters or clears it.
|
|
*/
|
|
rt_mutex_set_owner(lock, task);
|
|
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* Task blocks on lock.
|
|
*
|
|
* Prepare waiter and propagate pi chain
|
|
*
|
|
* This must be called with lock->wait_lock held and interrupts disabled
|
|
*/
|
|
static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
|
|
struct rt_mutex_waiter *waiter,
|
|
struct task_struct *task,
|
|
enum rtmutex_chainwalk chwalk)
|
|
{
|
|
struct task_struct *owner = rt_mutex_owner(lock);
|
|
struct rt_mutex_waiter *top_waiter = waiter;
|
|
struct rt_mutex *next_lock;
|
|
int chain_walk = 0, res;
|
|
|
|
lockdep_assert_held(&lock->wait_lock);
|
|
|
|
/*
|
|
* Early deadlock detection. We really don't want the task to
|
|
* enqueue on itself just to untangle the mess later. It's not
|
|
* only an optimization. We drop the locks, so another waiter
|
|
* can come in before the chain walk detects the deadlock. So
|
|
* the other will detect the deadlock and return -EDEADLOCK,
|
|
* which is wrong, as the other waiter is not in a deadlock
|
|
* situation.
|
|
*/
|
|
if (owner == task)
|
|
return -EDEADLK;
|
|
|
|
raw_spin_lock(&task->pi_lock);
|
|
waiter->task = task;
|
|
waiter->lock = lock;
|
|
waiter->prio = task->prio;
|
|
waiter->deadline = task->dl.deadline;
|
|
|
|
/* Get the top priority waiter on the lock */
|
|
if (rt_mutex_has_waiters(lock))
|
|
top_waiter = rt_mutex_top_waiter(lock);
|
|
rt_mutex_enqueue(lock, waiter);
|
|
|
|
task->pi_blocked_on = waiter;
|
|
|
|
raw_spin_unlock(&task->pi_lock);
|
|
|
|
if (!owner)
|
|
return 0;
|
|
|
|
raw_spin_lock(&owner->pi_lock);
|
|
if (waiter == rt_mutex_top_waiter(lock)) {
|
|
rt_mutex_dequeue_pi(owner, top_waiter);
|
|
rt_mutex_enqueue_pi(owner, waiter);
|
|
|
|
rt_mutex_adjust_prio(owner);
|
|
if (owner->pi_blocked_on)
|
|
chain_walk = 1;
|
|
} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
|
|
chain_walk = 1;
|
|
}
|
|
|
|
/* Store the lock on which owner is blocked or NULL */
|
|
next_lock = task_blocked_on_lock(owner);
|
|
|
|
raw_spin_unlock(&owner->pi_lock);
|
|
/*
|
|
* Even if full deadlock detection is on, if the owner is not
|
|
* blocked itself, we can avoid finding this out in the chain
|
|
* walk.
|
|
*/
|
|
if (!chain_walk || !next_lock)
|
|
return 0;
|
|
|
|
/*
|
|
* The owner can't disappear while holding a lock,
|
|
* so the owner struct is protected by wait_lock.
|
|
* Gets dropped in rt_mutex_adjust_prio_chain()!
|
|
*/
|
|
get_task_struct(owner);
|
|
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
|
|
res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
|
|
next_lock, waiter, task);
|
|
|
|
raw_spin_lock_irq(&lock->wait_lock);
|
|
|
|
return res;
|
|
}
|
|
|
|
/*
|
|
* Remove the top waiter from the current tasks pi waiter tree and
|
|
* queue it up.
|
|
*
|
|
* Called with lock->wait_lock held and interrupts disabled.
|
|
*/
|
|
static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
|
|
struct rt_mutex *lock)
|
|
{
|
|
struct rt_mutex_waiter *waiter;
|
|
|
|
raw_spin_lock(¤t->pi_lock);
|
|
|
|
waiter = rt_mutex_top_waiter(lock);
|
|
|
|
/*
|
|
* Remove it from current->pi_waiters and deboost.
|
|
*
|
|
* We must in fact deboost here in order to ensure we call
|
|
* rt_mutex_setprio() to update p->pi_top_task before the
|
|
* task unblocks.
|
|
*/
|
|
rt_mutex_dequeue_pi(current, waiter);
|
|
rt_mutex_adjust_prio(current);
|
|
|
|
/*
|
|
* As we are waking up the top waiter, and the waiter stays
|
|
* queued on the lock until it gets the lock, this lock
|
|
* obviously has waiters. Just set the bit here and this has
|
|
* the added benefit of forcing all new tasks into the
|
|
* slow path making sure no task of lower priority than
|
|
* the top waiter can steal this lock.
|
|
*/
|
|
lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
|
|
|
|
/*
|
|
* We deboosted before waking the top waiter task such that we don't
|
|
* run two tasks with the 'same' priority (and ensure the
|
|
* p->pi_top_task pointer points to a blocked task). This however can
|
|
* lead to priority inversion if we would get preempted after the
|
|
* deboost but before waking our donor task, hence the preempt_disable()
|
|
* before unlock.
|
|
*
|
|
* Pairs with preempt_enable() in rt_mutex_postunlock();
|
|
*/
|
|
preempt_disable();
|
|
wake_q_add(wake_q, waiter->task);
|
|
raw_spin_unlock(¤t->pi_lock);
|
|
}
|
|
|
|
/*
|
|
* Remove a waiter from a lock and give up
|
|
*
|
|
* Must be called with lock->wait_lock held and interrupts disabled. I must
|
|
* have just failed to try_to_take_rt_mutex().
|
|
*/
|
|
static void remove_waiter(struct rt_mutex *lock,
|
|
struct rt_mutex_waiter *waiter)
|
|
{
|
|
bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
|
|
struct task_struct *owner = rt_mutex_owner(lock);
|
|
struct rt_mutex *next_lock;
|
|
|
|
lockdep_assert_held(&lock->wait_lock);
|
|
|
|
raw_spin_lock(¤t->pi_lock);
|
|
rt_mutex_dequeue(lock, waiter);
|
|
current->pi_blocked_on = NULL;
|
|
raw_spin_unlock(¤t->pi_lock);
|
|
|
|
/*
|
|
* Only update priority if the waiter was the highest priority
|
|
* waiter of the lock and there is an owner to update.
|
|
*/
|
|
if (!owner || !is_top_waiter)
|
|
return;
|
|
|
|
raw_spin_lock(&owner->pi_lock);
|
|
|
|
rt_mutex_dequeue_pi(owner, waiter);
|
|
|
|
if (rt_mutex_has_waiters(lock))
|
|
rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
|
|
|
|
rt_mutex_adjust_prio(owner);
|
|
|
|
/* Store the lock on which owner is blocked or NULL */
|
|
next_lock = task_blocked_on_lock(owner);
|
|
|
|
raw_spin_unlock(&owner->pi_lock);
|
|
|
|
/*
|
|
* Don't walk the chain, if the owner task is not blocked
|
|
* itself.
|
|
*/
|
|
if (!next_lock)
|
|
return;
|
|
|
|
/* gets dropped in rt_mutex_adjust_prio_chain()! */
|
|
get_task_struct(owner);
|
|
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
|
|
rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
|
|
next_lock, NULL, current);
|
|
|
|
raw_spin_lock_irq(&lock->wait_lock);
|
|
}
|
|
|
|
/*
|
|
* Recheck the pi chain, in case we got a priority setting
|
|
*
|
|
* Called from sched_setscheduler
|
|
*/
|
|
void rt_mutex_adjust_pi(struct task_struct *task)
|
|
{
|
|
struct rt_mutex_waiter *waiter;
|
|
struct rt_mutex *next_lock;
|
|
unsigned long flags;
|
|
|
|
raw_spin_lock_irqsave(&task->pi_lock, flags);
|
|
|
|
waiter = task->pi_blocked_on;
|
|
if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
|
|
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
|
|
return;
|
|
}
|
|
next_lock = waiter->lock;
|
|
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
|
|
|
|
/* gets dropped in rt_mutex_adjust_prio_chain()! */
|
|
get_task_struct(task);
|
|
|
|
rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
|
|
next_lock, NULL, task);
|
|
}
|
|
|
|
void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
|
|
{
|
|
debug_rt_mutex_init_waiter(waiter);
|
|
RB_CLEAR_NODE(&waiter->pi_tree_entry);
|
|
RB_CLEAR_NODE(&waiter->tree_entry);
|
|
waiter->task = NULL;
|
|
}
|
|
|
|
/**
|
|
* __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
|
|
* @lock: the rt_mutex to take
|
|
* @state: the state the task should block in (TASK_INTERRUPTIBLE
|
|
* or TASK_UNINTERRUPTIBLE)
|
|
* @timeout: the pre-initialized and started timer, or NULL for none
|
|
* @waiter: the pre-initialized rt_mutex_waiter
|
|
*
|
|
* Must be called with lock->wait_lock held and interrupts disabled
|
|
*/
|
|
static int __sched
|
|
__rt_mutex_slowlock(struct rt_mutex *lock, int state,
|
|
struct hrtimer_sleeper *timeout,
|
|
struct rt_mutex_waiter *waiter)
|
|
{
|
|
int ret = 0;
|
|
|
|
for (;;) {
|
|
/* Try to acquire the lock: */
|
|
if (try_to_take_rt_mutex(lock, current, waiter))
|
|
break;
|
|
|
|
/*
|
|
* TASK_INTERRUPTIBLE checks for signals and
|
|
* timeout. Ignored otherwise.
|
|
*/
|
|
if (likely(state == TASK_INTERRUPTIBLE)) {
|
|
/* Signal pending? */
|
|
if (signal_pending(current))
|
|
ret = -EINTR;
|
|
if (timeout && !timeout->task)
|
|
ret = -ETIMEDOUT;
|
|
if (ret)
|
|
break;
|
|
}
|
|
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
|
|
debug_rt_mutex_print_deadlock(waiter);
|
|
|
|
schedule();
|
|
|
|
raw_spin_lock_irq(&lock->wait_lock);
|
|
set_current_state(state);
|
|
}
|
|
|
|
__set_current_state(TASK_RUNNING);
|
|
return ret;
|
|
}
|
|
|
|
static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
|
|
struct rt_mutex_waiter *w)
|
|
{
|
|
/*
|
|
* If the result is not -EDEADLOCK or the caller requested
|
|
* deadlock detection, nothing to do here.
|
|
*/
|
|
if (res != -EDEADLOCK || detect_deadlock)
|
|
return;
|
|
|
|
/*
|
|
* Yell lowdly and stop the task right here.
|
|
*/
|
|
rt_mutex_print_deadlock(w);
|
|
while (1) {
|
|
set_current_state(TASK_INTERRUPTIBLE);
|
|
schedule();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Slow path lock function:
|
|
*/
|
|
static int __sched
|
|
rt_mutex_slowlock(struct rt_mutex *lock, int state,
|
|
struct hrtimer_sleeper *timeout,
|
|
enum rtmutex_chainwalk chwalk)
|
|
{
|
|
struct rt_mutex_waiter waiter;
|
|
unsigned long flags;
|
|
int ret = 0;
|
|
|
|
rt_mutex_init_waiter(&waiter);
|
|
|
|
/*
|
|
* Technically we could use raw_spin_[un]lock_irq() here, but this can
|
|
* be called in early boot if the cmpxchg() fast path is disabled
|
|
* (debug, no architecture support). In this case we will acquire the
|
|
* rtmutex with lock->wait_lock held. But we cannot unconditionally
|
|
* enable interrupts in that early boot case. So we need to use the
|
|
* irqsave/restore variants.
|
|
*/
|
|
raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
|
|
|
/* Try to acquire the lock again: */
|
|
if (try_to_take_rt_mutex(lock, current, NULL)) {
|
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
|
return 0;
|
|
}
|
|
|
|
set_current_state(state);
|
|
|
|
/* Setup the timer, when timeout != NULL */
|
|
if (unlikely(timeout))
|
|
hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
|
|
|
|
ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
|
|
|
|
if (likely(!ret))
|
|
/* sleep on the mutex */
|
|
ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
|
|
|
|
if (unlikely(ret)) {
|
|
__set_current_state(TASK_RUNNING);
|
|
remove_waiter(lock, &waiter);
|
|
rt_mutex_handle_deadlock(ret, chwalk, &waiter);
|
|
}
|
|
|
|
/*
|
|
* try_to_take_rt_mutex() sets the waiter bit
|
|
* unconditionally. We might have to fix that up.
|
|
*/
|
|
fixup_rt_mutex_waiters(lock);
|
|
|
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
|
|
|
/* Remove pending timer: */
|
|
if (unlikely(timeout))
|
|
hrtimer_cancel(&timeout->timer);
|
|
|
|
debug_rt_mutex_free_waiter(&waiter);
|
|
|
|
return ret;
|
|
}
|
|
|
|
static inline int __rt_mutex_slowtrylock(struct rt_mutex *lock)
|
|
{
|
|
int ret = try_to_take_rt_mutex(lock, current, NULL);
|
|
|
|
/*
|
|
* try_to_take_rt_mutex() sets the lock waiters bit
|
|
* unconditionally. Clean this up.
|
|
*/
|
|
fixup_rt_mutex_waiters(lock);
|
|
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Slow path try-lock function:
|
|
*/
|
|
static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
|
|
{
|
|
unsigned long flags;
|
|
int ret;
|
|
|
|
/*
|
|
* If the lock already has an owner we fail to get the lock.
|
|
* This can be done without taking the @lock->wait_lock as
|
|
* it is only being read, and this is a trylock anyway.
|
|
*/
|
|
if (rt_mutex_owner(lock))
|
|
return 0;
|
|
|
|
/*
|
|
* The mutex has currently no owner. Lock the wait lock and try to
|
|
* acquire the lock. We use irqsave here to support early boot calls.
|
|
*/
|
|
raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
|
|
|
ret = __rt_mutex_slowtrylock(lock);
|
|
|
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
|
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Slow path to release a rt-mutex.
|
|
*
|
|
* Return whether the current task needs to call rt_mutex_postunlock().
|
|
*/
|
|
static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
|
|
struct wake_q_head *wake_q)
|
|
{
|
|
unsigned long flags;
|
|
|
|
/* irqsave required to support early boot calls */
|
|
raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
|
|
|
debug_rt_mutex_unlock(lock);
|
|
|
|
/*
|
|
* We must be careful here if the fast path is enabled. If we
|
|
* have no waiters queued we cannot set owner to NULL here
|
|
* because of:
|
|
*
|
|
* foo->lock->owner = NULL;
|
|
* rtmutex_lock(foo->lock); <- fast path
|
|
* free = atomic_dec_and_test(foo->refcnt);
|
|
* rtmutex_unlock(foo->lock); <- fast path
|
|
* if (free)
|
|
* kfree(foo);
|
|
* raw_spin_unlock(foo->lock->wait_lock);
|
|
*
|
|
* So for the fastpath enabled kernel:
|
|
*
|
|
* Nothing can set the waiters bit as long as we hold
|
|
* lock->wait_lock. So we do the following sequence:
|
|
*
|
|
* owner = rt_mutex_owner(lock);
|
|
* clear_rt_mutex_waiters(lock);
|
|
* raw_spin_unlock(&lock->wait_lock);
|
|
* if (cmpxchg(&lock->owner, owner, 0) == owner)
|
|
* return;
|
|
* goto retry;
|
|
*
|
|
* The fastpath disabled variant is simple as all access to
|
|
* lock->owner is serialized by lock->wait_lock:
|
|
*
|
|
* lock->owner = NULL;
|
|
* raw_spin_unlock(&lock->wait_lock);
|
|
*/
|
|
while (!rt_mutex_has_waiters(lock)) {
|
|
/* Drops lock->wait_lock ! */
|
|
if (unlock_rt_mutex_safe(lock, flags) == true)
|
|
return false;
|
|
/* Relock the rtmutex and try again */
|
|
raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
|
}
|
|
|
|
/*
|
|
* The wakeup next waiter path does not suffer from the above
|
|
* race. See the comments there.
|
|
*
|
|
* Queue the next waiter for wakeup once we release the wait_lock.
|
|
*/
|
|
mark_wakeup_next_waiter(wake_q, lock);
|
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
|
|
|
return true; /* call rt_mutex_postunlock() */
|
|
}
|
|
|
|
/*
|
|
* debug aware fast / slowpath lock,trylock,unlock
|
|
*
|
|
* The atomic acquire/release ops are compiled away, when either the
|
|
* architecture does not support cmpxchg or when debugging is enabled.
|
|
*/
|
|
static inline int
|
|
rt_mutex_fastlock(struct rt_mutex *lock, int state,
|
|
int (*slowfn)(struct rt_mutex *lock, int state,
|
|
struct hrtimer_sleeper *timeout,
|
|
enum rtmutex_chainwalk chwalk))
|
|
{
|
|
if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
|
|
return 0;
|
|
|
|
return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
|
|
}
|
|
|
|
static inline int
|
|
rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
|
|
struct hrtimer_sleeper *timeout,
|
|
enum rtmutex_chainwalk chwalk,
|
|
int (*slowfn)(struct rt_mutex *lock, int state,
|
|
struct hrtimer_sleeper *timeout,
|
|
enum rtmutex_chainwalk chwalk))
|
|
{
|
|
if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
|
|
likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
|
|
return 0;
|
|
|
|
return slowfn(lock, state, timeout, chwalk);
|
|
}
|
|
|
|
static inline int
|
|
rt_mutex_fasttrylock(struct rt_mutex *lock,
|
|
int (*slowfn)(struct rt_mutex *lock))
|
|
{
|
|
if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
|
|
return 1;
|
|
|
|
return slowfn(lock);
|
|
}
|
|
|
|
/*
|
|
* Performs the wakeup of the the top-waiter and re-enables preemption.
|
|
*/
|
|
void rt_mutex_postunlock(struct wake_q_head *wake_q)
|
|
{
|
|
wake_up_q(wake_q);
|
|
|
|
/* Pairs with preempt_disable() in rt_mutex_slowunlock() */
|
|
preempt_enable();
|
|
}
|
|
|
|
static inline void
|
|
rt_mutex_fastunlock(struct rt_mutex *lock,
|
|
bool (*slowfn)(struct rt_mutex *lock,
|
|
struct wake_q_head *wqh))
|
|
{
|
|
DEFINE_WAKE_Q(wake_q);
|
|
|
|
if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
|
|
return;
|
|
|
|
if (slowfn(lock, &wake_q))
|
|
rt_mutex_postunlock(&wake_q);
|
|
}
|
|
|
|
static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
|
|
{
|
|
might_sleep();
|
|
|
|
mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
|
|
rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
|
|
}
|
|
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
|
/**
|
|
* rt_mutex_lock_nested - lock a rt_mutex
|
|
*
|
|
* @lock: the rt_mutex to be locked
|
|
* @subclass: the lockdep subclass
|
|
*/
|
|
void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
|
|
{
|
|
__rt_mutex_lock(lock, subclass);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
|
|
|
|
#else /* !CONFIG_DEBUG_LOCK_ALLOC */
|
|
|
|
/**
|
|
* rt_mutex_lock - lock a rt_mutex
|
|
*
|
|
* @lock: the rt_mutex to be locked
|
|
*/
|
|
void __sched rt_mutex_lock(struct rt_mutex *lock)
|
|
{
|
|
__rt_mutex_lock(lock, 0);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rt_mutex_lock);
|
|
#endif
|
|
|
|
/**
|
|
* rt_mutex_lock_interruptible - lock a rt_mutex interruptible
|
|
*
|
|
* @lock: the rt_mutex to be locked
|
|
*
|
|
* Returns:
|
|
* 0 on success
|
|
* -EINTR when interrupted by a signal
|
|
*/
|
|
int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
|
|
{
|
|
int ret;
|
|
|
|
might_sleep();
|
|
|
|
mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
|
|
ret = rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
|
|
if (ret)
|
|
mutex_release(&lock->dep_map, _RET_IP_);
|
|
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
|
|
|
|
/*
|
|
* Futex variant, must not use fastpath.
|
|
*/
|
|
int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
|
|
{
|
|
return rt_mutex_slowtrylock(lock);
|
|
}
|
|
|
|
int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
|
|
{
|
|
return __rt_mutex_slowtrylock(lock);
|
|
}
|
|
|
|
/**
|
|
* rt_mutex_timed_lock - lock a rt_mutex interruptible
|
|
* the timeout structure is provided
|
|
* by the caller
|
|
*
|
|
* @lock: the rt_mutex to be locked
|
|
* @timeout: timeout structure or NULL (no timeout)
|
|
*
|
|
* Returns:
|
|
* 0 on success
|
|
* -EINTR when interrupted by a signal
|
|
* -ETIMEDOUT when the timeout expired
|
|
*/
|
|
int
|
|
rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
|
|
{
|
|
int ret;
|
|
|
|
might_sleep();
|
|
|
|
mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
|
|
ret = rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
|
|
RT_MUTEX_MIN_CHAINWALK,
|
|
rt_mutex_slowlock);
|
|
if (ret)
|
|
mutex_release(&lock->dep_map, _RET_IP_);
|
|
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
|
|
|
|
/**
|
|
* rt_mutex_trylock - try to lock a rt_mutex
|
|
*
|
|
* @lock: the rt_mutex to be locked
|
|
*
|
|
* This function can only be called in thread context. It's safe to
|
|
* call it from atomic regions, but not from hard interrupt or soft
|
|
* interrupt context.
|
|
*
|
|
* Returns 1 on success and 0 on contention
|
|
*/
|
|
int __sched rt_mutex_trylock(struct rt_mutex *lock)
|
|
{
|
|
int ret;
|
|
|
|
if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
|
|
return 0;
|
|
|
|
ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
|
|
if (ret)
|
|
mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
|
|
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL_GPL(rt_mutex_trylock);
|
|
|
|
/**
|
|
* rt_mutex_unlock - unlock a rt_mutex
|
|
*
|
|
* @lock: the rt_mutex to be unlocked
|
|
*/
|
|
void __sched rt_mutex_unlock(struct rt_mutex *lock)
|
|
{
|
|
mutex_release(&lock->dep_map, _RET_IP_);
|
|
rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rt_mutex_unlock);
|
|
|
|
/**
|
|
* Futex variant, that since futex variants do not use the fast-path, can be
|
|
* simple and will not need to retry.
|
|
*/
|
|
bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
|
|
struct wake_q_head *wake_q)
|
|
{
|
|
lockdep_assert_held(&lock->wait_lock);
|
|
|
|
debug_rt_mutex_unlock(lock);
|
|
|
|
if (!rt_mutex_has_waiters(lock)) {
|
|
lock->owner = NULL;
|
|
return false; /* done */
|
|
}
|
|
|
|
/*
|
|
* We've already deboosted, mark_wakeup_next_waiter() will
|
|
* retain preempt_disabled when we drop the wait_lock, to
|
|
* avoid inversion prior to the wakeup. preempt_disable()
|
|
* therein pairs with rt_mutex_postunlock().
|
|
*/
|
|
mark_wakeup_next_waiter(wake_q, lock);
|
|
|
|
return true; /* call postunlock() */
|
|
}
|
|
|
|
void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
|
|
{
|
|
DEFINE_WAKE_Q(wake_q);
|
|
unsigned long flags;
|
|
bool postunlock;
|
|
|
|
raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
|
postunlock = __rt_mutex_futex_unlock(lock, &wake_q);
|
|
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
|
|
|
if (postunlock)
|
|
rt_mutex_postunlock(&wake_q);
|
|
}
|
|
|
|
/**
|
|
* rt_mutex_destroy - mark a mutex unusable
|
|
* @lock: the mutex to be destroyed
|
|
*
|
|
* This function marks the mutex uninitialized, and any subsequent
|
|
* use of the mutex is forbidden. The mutex must not be locked when
|
|
* this function is called.
|
|
*/
|
|
void rt_mutex_destroy(struct rt_mutex *lock)
|
|
{
|
|
WARN_ON(rt_mutex_is_locked(lock));
|
|
#ifdef CONFIG_DEBUG_RT_MUTEXES
|
|
lock->magic = NULL;
|
|
#endif
|
|
}
|
|
EXPORT_SYMBOL_GPL(rt_mutex_destroy);
|
|
|
|
/**
|
|
* __rt_mutex_init - initialize the rt lock
|
|
*
|
|
* @lock: the rt lock to be initialized
|
|
*
|
|
* Initialize the rt lock to unlocked state.
|
|
*
|
|
* Initializing of a locked rt lock is not allowed
|
|
*/
|
|
void __rt_mutex_init(struct rt_mutex *lock, const char *name,
|
|
struct lock_class_key *key)
|
|
{
|
|
lock->owner = NULL;
|
|
raw_spin_lock_init(&lock->wait_lock);
|
|
lock->waiters = RB_ROOT_CACHED;
|
|
|
|
if (name && key)
|
|
debug_rt_mutex_init(lock, name, key);
|
|
}
|
|
EXPORT_SYMBOL_GPL(__rt_mutex_init);
|
|
|
|
/**
|
|
* rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
|
|
* proxy owner
|
|
*
|
|
* @lock: the rt_mutex to be locked
|
|
* @proxy_owner:the task to set as owner
|
|
*
|
|
* No locking. Caller has to do serializing itself
|
|
*
|
|
* Special API call for PI-futex support. This initializes the rtmutex and
|
|
* assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
|
|
* possible at this point because the pi_state which contains the rtmutex
|
|
* is not yet visible to other tasks.
|
|
*/
|
|
void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
|
|
struct task_struct *proxy_owner)
|
|
{
|
|
__rt_mutex_init(lock, NULL, NULL);
|
|
debug_rt_mutex_proxy_lock(lock, proxy_owner);
|
|
rt_mutex_set_owner(lock, proxy_owner);
|
|
}
|
|
|
|
/**
|
|
* rt_mutex_proxy_unlock - release a lock on behalf of owner
|
|
*
|
|
* @lock: the rt_mutex to be locked
|
|
*
|
|
* No locking. Caller has to do serializing itself
|
|
*
|
|
* Special API call for PI-futex support. This merrily cleans up the rtmutex
|
|
* (debugging) state. Concurrent operations on this rt_mutex are not
|
|
* possible because it belongs to the pi_state which is about to be freed
|
|
* and it is not longer visible to other tasks.
|
|
*/
|
|
void rt_mutex_proxy_unlock(struct rt_mutex *lock,
|
|
struct task_struct *proxy_owner)
|
|
{
|
|
debug_rt_mutex_proxy_unlock(lock);
|
|
rt_mutex_set_owner(lock, NULL);
|
|
}
|
|
|
|
/**
|
|
* __rt_mutex_start_proxy_lock() - Start lock acquisition for another task
|
|
* @lock: the rt_mutex to take
|
|
* @waiter: the pre-initialized rt_mutex_waiter
|
|
* @task: the task to prepare
|
|
*
|
|
* Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
|
|
* detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
|
|
*
|
|
* NOTE: does _NOT_ remove the @waiter on failure; must either call
|
|
* rt_mutex_wait_proxy_lock() or rt_mutex_cleanup_proxy_lock() after this.
|
|
*
|
|
* Returns:
|
|
* 0 - task blocked on lock
|
|
* 1 - acquired the lock for task, caller should wake it up
|
|
* <0 - error
|
|
*
|
|
* Special API call for PI-futex support.
|
|
*/
|
|
int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
|
|
struct rt_mutex_waiter *waiter,
|
|
struct task_struct *task)
|
|
{
|
|
int ret;
|
|
|
|
lockdep_assert_held(&lock->wait_lock);
|
|
|
|
if (try_to_take_rt_mutex(lock, task, NULL))
|
|
return 1;
|
|
|
|
/* We enforce deadlock detection for futexes */
|
|
ret = task_blocks_on_rt_mutex(lock, waiter, task,
|
|
RT_MUTEX_FULL_CHAINWALK);
|
|
|
|
if (ret && !rt_mutex_owner(lock)) {
|
|
/*
|
|
* Reset the return value. We might have
|
|
* returned with -EDEADLK and the owner
|
|
* released the lock while we were walking the
|
|
* pi chain. Let the waiter sort it out.
|
|
*/
|
|
ret = 0;
|
|
}
|
|
|
|
debug_rt_mutex_print_deadlock(waiter);
|
|
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* rt_mutex_start_proxy_lock() - Start lock acquisition for another task
|
|
* @lock: the rt_mutex to take
|
|
* @waiter: the pre-initialized rt_mutex_waiter
|
|
* @task: the task to prepare
|
|
*
|
|
* Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
|
|
* detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
|
|
*
|
|
* NOTE: unlike __rt_mutex_start_proxy_lock this _DOES_ remove the @waiter
|
|
* on failure.
|
|
*
|
|
* Returns:
|
|
* 0 - task blocked on lock
|
|
* 1 - acquired the lock for task, caller should wake it up
|
|
* <0 - error
|
|
*
|
|
* Special API call for PI-futex support.
|
|
*/
|
|
int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
|
|
struct rt_mutex_waiter *waiter,
|
|
struct task_struct *task)
|
|
{
|
|
int ret;
|
|
|
|
raw_spin_lock_irq(&lock->wait_lock);
|
|
ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
|
|
if (unlikely(ret))
|
|
remove_waiter(lock, waiter);
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* rt_mutex_next_owner - return the next owner of the lock
|
|
*
|
|
* @lock: the rt lock query
|
|
*
|
|
* Returns the next owner of the lock or NULL
|
|
*
|
|
* Caller has to serialize against other accessors to the lock
|
|
* itself.
|
|
*
|
|
* Special API call for PI-futex support
|
|
*/
|
|
struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
|
|
{
|
|
if (!rt_mutex_has_waiters(lock))
|
|
return NULL;
|
|
|
|
return rt_mutex_top_waiter(lock)->task;
|
|
}
|
|
|
|
/**
|
|
* rt_mutex_wait_proxy_lock() - Wait for lock acquisition
|
|
* @lock: the rt_mutex we were woken on
|
|
* @to: the timeout, null if none. hrtimer should already have
|
|
* been started.
|
|
* @waiter: the pre-initialized rt_mutex_waiter
|
|
*
|
|
* Wait for the the lock acquisition started on our behalf by
|
|
* rt_mutex_start_proxy_lock(). Upon failure, the caller must call
|
|
* rt_mutex_cleanup_proxy_lock().
|
|
*
|
|
* Returns:
|
|
* 0 - success
|
|
* <0 - error, one of -EINTR, -ETIMEDOUT
|
|
*
|
|
* Special API call for PI-futex support
|
|
*/
|
|
int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
|
|
struct hrtimer_sleeper *to,
|
|
struct rt_mutex_waiter *waiter)
|
|
{
|
|
int ret;
|
|
|
|
raw_spin_lock_irq(&lock->wait_lock);
|
|
/* sleep on the mutex */
|
|
set_current_state(TASK_INTERRUPTIBLE);
|
|
ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
|
|
/*
|
|
* try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
|
|
* have to fix that up.
|
|
*/
|
|
fixup_rt_mutex_waiters(lock);
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
|
|
* @lock: the rt_mutex we were woken on
|
|
* @waiter: the pre-initialized rt_mutex_waiter
|
|
*
|
|
* Attempt to clean up after a failed __rt_mutex_start_proxy_lock() or
|
|
* rt_mutex_wait_proxy_lock().
|
|
*
|
|
* Unless we acquired the lock; we're still enqueued on the wait-list and can
|
|
* in fact still be granted ownership until we're removed. Therefore we can
|
|
* find we are in fact the owner and must disregard the
|
|
* rt_mutex_wait_proxy_lock() failure.
|
|
*
|
|
* Returns:
|
|
* true - did the cleanup, we done.
|
|
* false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
|
|
* caller should disregards its return value.
|
|
*
|
|
* Special API call for PI-futex support
|
|
*/
|
|
bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
|
|
struct rt_mutex_waiter *waiter)
|
|
{
|
|
bool cleanup = false;
|
|
|
|
raw_spin_lock_irq(&lock->wait_lock);
|
|
/*
|
|
* Do an unconditional try-lock, this deals with the lock stealing
|
|
* state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
|
|
* sets a NULL owner.
|
|
*
|
|
* We're not interested in the return value, because the subsequent
|
|
* test on rt_mutex_owner() will infer that. If the trylock succeeded,
|
|
* we will own the lock and it will have removed the waiter. If we
|
|
* failed the trylock, we're still not owner and we need to remove
|
|
* ourselves.
|
|
*/
|
|
try_to_take_rt_mutex(lock, current, waiter);
|
|
/*
|
|
* Unless we're the owner; we're still enqueued on the wait_list.
|
|
* So check if we became owner, if not, take us off the wait_list.
|
|
*/
|
|
if (rt_mutex_owner(lock) != current) {
|
|
remove_waiter(lock, waiter);
|
|
cleanup = true;
|
|
}
|
|
/*
|
|
* try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
|
|
* have to fix that up.
|
|
*/
|
|
fixup_rt_mutex_waiters(lock);
|
|
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
|
|
return cleanup;
|
|
}
|