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![Peter Zijlstra](/assets/img/avatar_default.png)
Markus reported that the glibc/nptl/tst-robustpi8 test was failing after commit:cfafcd117d
("futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock()") The following trace shows the problem: ld-linux-x86-64-2161 [019] .... 410.760971: SyS_futex: 00007ffbeb76b028: 80000875 op=FUTEX_LOCK_PI ld-linux-x86-64-2161 [019] ...1 410.760972: lock_pi_update_atomic: 00007ffbeb76b028: curval=80000875 uval=80000875 newval=80000875 ret=0 ld-linux-x86-64-2165 [011] .... 410.760978: SyS_futex: 00007ffbeb76b028: 80000875 op=FUTEX_UNLOCK_PI ld-linux-x86-64-2165 [011] d..1 410.760979: do_futex: 00007ffbeb76b028: curval=80000875 uval=80000875 newval=80000871 ret=0 ld-linux-x86-64-2165 [011] .... 410.760980: SyS_futex: 00007ffbeb76b028: 80000871 ret=0000 ld-linux-x86-64-2161 [019] .... 410.760980: SyS_futex: 00007ffbeb76b028: 80000871 ret=ETIMEDOUT Task 2165 does an UNLOCK_PI, assigning the lock to the waiter task 2161 which then returns with -ETIMEDOUT. That wrecks the lock state, because now the owner isn't aware it acquired the lock and removes the pending robust list entry. If 2161 is killed, the robust list will not clear out this futex and the subsequent acquire on this futex will then (correctly) result in -ESRCH which is unexpected by glibc, triggers an internal assertion and dies. Task 2161 Task 2165 rt_mutex_wait_proxy_lock() timeout(); /* T2161 is still queued in the waiter list */ return -ETIMEDOUT; futex_unlock_pi() spin_lock(hb->lock); rtmutex_unlock() remove_rtmutex_waiter(T2161); mark_lock_available(); /* Make the next waiter owner of the user space side */ futex_uval = 2161; spin_unlock(hb->lock); spin_lock(hb->lock); rt_mutex_cleanup_proxy_lock() if (rtmutex_owner() !== current) ... return FAIL; .... return -ETIMEOUT; This means that rt_mutex_cleanup_proxy_lock() needs to call try_to_take_rt_mutex() so it can take over the rtmutex correctly which was assigned by the waker. If the rtmutex is owned by some other task then this call is harmless and just confirmes that the waiter is not able to acquire it. While there, fix what looks like a merge error which resulted in rt_mutex_cleanup_proxy_lock() having two calls to fixup_rt_mutex_waiters() and rt_mutex_wait_proxy_lock() not having any. Both should have one, since both potentially touch the waiter list. Fixes:38d589f2fd
("futex,rt_mutex: Restructure rt_mutex_finish_proxy_lock()") Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de> Bug-Spotted-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Florian Weimer <fweimer@redhat.com> Cc: Darren Hart <dvhart@infradead.org> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Markus Trippelsdorf <markus@trippelsdorf.de> Link: http://lkml.kernel.org/r/20170519154850.mlomgdsd26drq5j6@hirez.programming.kicks-ass.net Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
1855 lines
49 KiB
C
1855 lines
49 KiB
C
/*
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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.txt 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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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_node;
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struct rb_node *parent = NULL;
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struct rt_mutex_waiter *entry;
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int leftmost = 1;
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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 = 0;
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}
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}
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if (leftmost)
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lock->waiters_leftmost = &waiter->tree_entry;
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rb_link_node(&waiter->tree_entry, parent, link);
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rb_insert_color(&waiter->tree_entry, &lock->waiters);
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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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if (lock->waiters_leftmost == &waiter->tree_entry)
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lock->waiters_leftmost = rb_next(&waiter->tree_entry);
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rb_erase(&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_node;
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struct rb_node *parent = NULL;
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struct rt_mutex_waiter *entry;
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int leftmost = 1;
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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 = 0;
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}
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}
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if (leftmost)
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task->pi_waiters_leftmost = &waiter->pi_tree_entry;
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rb_link_node(&waiter->pi_tree_entry, parent, link);
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rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
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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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if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
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task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
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rb_erase(&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
|
|
* locking protected by calling
|
|
* code
|
|
* again:
|
|
* loop_sanity_check();
|
|
* retry:
|
|
* [1] lock(task->pi_lock); [R] acquire [P]
|
|
* [2] waiter = task->pi_blocked_on; [P]
|
|
* [3] check_exit_conditions_1(); [P]
|
|
* [4] lock = waiter->lock; [P]
|
|
* [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
|
|
* unlock(task->pi_lock); release [P]
|
|
* goto retry;
|
|
* }
|
|
* [6] check_exit_conditions_2(); [P] + [L]
|
|
* [7] requeue_lock_waiter(lock, waiter); [P] + [L]
|
|
* [8] unlock(task->pi_lock); release [P]
|
|
* put_task_struct(task); release [R]
|
|
* [9] check_exit_conditions_3(); [L]
|
|
* [10] task = owner(lock); [L]
|
|
* get_task_struct(task); [L] acquire [R]
|
|
* lock(task->pi_lock); [L] acquire [P]
|
|
* [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
|
|
* [12] check_exit_conditions_4(); [P] + [L]
|
|
* [13] unlock(task->pi_lock); release [P]
|
|
* unlock(lock->wait_lock); release [L]
|
|
* goto again;
|
|
*/
|
|
static int rt_mutex_adjust_prio_chain(struct task_struct *task,
|
|
enum rtmutex_chainwalk chwalk,
|
|
struct rt_mutex *orig_lock,
|
|
struct rt_mutex *next_lock,
|
|
struct rt_mutex_waiter *orig_waiter,
|
|
struct task_struct *top_task)
|
|
{
|
|
struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
|
|
struct rt_mutex_waiter *prerequeue_top_waiter;
|
|
int ret = 0, depth = 0;
|
|
struct rt_mutex *lock;
|
|
bool detect_deadlock;
|
|
bool requeue = true;
|
|
|
|
detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
|
|
|
|
/*
|
|
* The (de)boosting is a step by step approach with a lot of
|
|
* pitfalls. We want this to be preemptible and we want hold a
|
|
* maximum of two locks per step. So we have to check
|
|
* carefully whether things change under us.
|
|
*/
|
|
again:
|
|
/*
|
|
* We limit the lock chain length for each invocation.
|
|
*/
|
|
if (++depth > max_lock_depth) {
|
|
static int prev_max;
|
|
|
|
/*
|
|
* 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 = rt_mutex_owner(lock);
|
|
get_task_struct(task);
|
|
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 = rt_mutex_owner(lock);
|
|
get_task_struct(task);
|
|
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);
|
|
rt_mutex_adjust_prio(task);
|
|
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);
|
|
if (rt_mutex_has_waiters(lock))
|
|
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;
|
|
}
|
|
|
|
/*
|
|
* 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 = 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);
|
|
|
|
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);
|
|
}
|
|
|
|
/**
|
|
* rt_mutex_lock - lock a rt_mutex
|
|
*
|
|
* @lock: the rt_mutex to be locked
|
|
*/
|
|
void __sched rt_mutex_lock(struct rt_mutex *lock)
|
|
{
|
|
might_sleep();
|
|
|
|
rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rt_mutex_lock);
|
|
|
|
/**
|
|
* 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)
|
|
{
|
|
might_sleep();
|
|
|
|
return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
|
|
}
|
|
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);
|
|
}
|
|
|
|
/**
|
|
* 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)
|
|
{
|
|
might_sleep();
|
|
|
|
return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
|
|
RT_MUTEX_MIN_CHAINWALK,
|
|
rt_mutex_slowlock);
|
|
}
|
|
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)
|
|
{
|
|
if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
|
|
return 0;
|
|
|
|
return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
|
|
}
|
|
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)
|
|
{
|
|
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);
|
|
bool postunlock;
|
|
|
|
raw_spin_lock_irq(&lock->wait_lock);
|
|
postunlock = __rt_mutex_futex_unlock(lock, &wake_q);
|
|
raw_spin_unlock_irq(&lock->wait_lock);
|
|
|
|
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)
|
|
{
|
|
lock->owner = NULL;
|
|
raw_spin_lock_init(&lock->wait_lock);
|
|
lock->waiters = RB_ROOT;
|
|
lock->waiters_leftmost = NULL;
|
|
|
|
debug_rt_mutex_init(lock, name);
|
|
}
|
|
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);
|
|
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);
|
|
}
|
|
|
|
int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
|
|
struct rt_mutex_waiter *waiter,
|
|
struct task_struct *task)
|
|
{
|
|
int ret;
|
|
|
|
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;
|
|
}
|
|
|
|
if (unlikely(ret))
|
|
remove_waiter(lock, waiter);
|
|
|
|
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
|
|
*
|
|
* Returns:
|
|
* 0 - task blocked on lock
|
|
* 1 - acquired the lock for task, caller should wake it up
|
|
* <0 - error
|
|
*
|
|
* Special API call for FUTEX_REQUEUE_PI 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);
|
|
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_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;
|
|
}
|