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![Peter Zijlstra](/assets/img/avatar_default.png)
Move all the requeue bits into their own file. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: André Almeida <andrealmeid@collabora.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: André Almeida <andrealmeid@collabora.com> Link: https://lore.kernel.org/r/20210923171111.300673-14-andrealmeid@collabora.com
897 lines
27 KiB
C
897 lines
27 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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#include <linux/sched/signal.h>
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#include "futex.h"
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#include "../locking/rtmutex_common.h"
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/*
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* On PREEMPT_RT, the hash bucket lock is a 'sleeping' spinlock with an
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* underlying rtmutex. The task which is about to be requeued could have
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* just woken up (timeout, signal). After the wake up the task has to
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* acquire hash bucket lock, which is held by the requeue code. As a task
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* can only be blocked on _ONE_ rtmutex at a time, the proxy lock blocking
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* and the hash bucket lock blocking would collide and corrupt state.
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*
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* On !PREEMPT_RT this is not a problem and everything could be serialized
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* on hash bucket lock, but aside of having the benefit of common code,
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* this allows to avoid doing the requeue when the task is already on the
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* way out and taking the hash bucket lock of the original uaddr1 when the
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* requeue has been completed.
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*
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* The following state transitions are valid:
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*
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* On the waiter side:
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* Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_IGNORE
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* Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_WAIT
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*
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* On the requeue side:
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* Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_INPROGRESS
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* Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_DONE/LOCKED
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* Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_NONE (requeue failed)
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* Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_DONE/LOCKED
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* Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_IGNORE (requeue failed)
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*
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* The requeue side ignores a waiter with state Q_REQUEUE_PI_IGNORE as this
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* signals that the waiter is already on the way out. It also means that
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* the waiter is still on the 'wait' futex, i.e. uaddr1.
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*
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* The waiter side signals early wakeup to the requeue side either through
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* setting state to Q_REQUEUE_PI_IGNORE or to Q_REQUEUE_PI_WAIT depending
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* on the current state. In case of Q_REQUEUE_PI_IGNORE it can immediately
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* proceed to take the hash bucket lock of uaddr1. If it set state to WAIT,
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* which means the wakeup is interleaving with a requeue in progress it has
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* to wait for the requeue side to change the state. Either to DONE/LOCKED
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* or to IGNORE. DONE/LOCKED means the waiter q is now on the uaddr2 futex
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* and either blocked (DONE) or has acquired it (LOCKED). IGNORE is set by
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* the requeue side when the requeue attempt failed via deadlock detection
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* and therefore the waiter q is still on the uaddr1 futex.
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*/
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enum {
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Q_REQUEUE_PI_NONE = 0,
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Q_REQUEUE_PI_IGNORE,
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Q_REQUEUE_PI_IN_PROGRESS,
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Q_REQUEUE_PI_WAIT,
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Q_REQUEUE_PI_DONE,
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Q_REQUEUE_PI_LOCKED,
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};
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const struct futex_q futex_q_init = {
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/* list gets initialized in futex_queue()*/
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.key = FUTEX_KEY_INIT,
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.bitset = FUTEX_BITSET_MATCH_ANY,
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.requeue_state = ATOMIC_INIT(Q_REQUEUE_PI_NONE),
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};
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/**
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* requeue_futex() - Requeue a futex_q from one hb to another
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* @q: the futex_q to requeue
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* @hb1: the source hash_bucket
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* @hb2: the target hash_bucket
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* @key2: the new key for the requeued futex_q
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*/
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static inline
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void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
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struct futex_hash_bucket *hb2, union futex_key *key2)
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{
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/*
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* If key1 and key2 hash to the same bucket, no need to
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* requeue.
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*/
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if (likely(&hb1->chain != &hb2->chain)) {
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plist_del(&q->list, &hb1->chain);
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futex_hb_waiters_dec(hb1);
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futex_hb_waiters_inc(hb2);
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plist_add(&q->list, &hb2->chain);
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q->lock_ptr = &hb2->lock;
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}
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q->key = *key2;
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}
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static inline bool futex_requeue_pi_prepare(struct futex_q *q,
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struct futex_pi_state *pi_state)
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{
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int old, new;
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/*
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* Set state to Q_REQUEUE_PI_IN_PROGRESS unless an early wakeup has
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* already set Q_REQUEUE_PI_IGNORE to signal that requeue should
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* ignore the waiter.
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*/
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old = atomic_read_acquire(&q->requeue_state);
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do {
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if (old == Q_REQUEUE_PI_IGNORE)
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return false;
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/*
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* futex_proxy_trylock_atomic() might have set it to
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* IN_PROGRESS and a interleaved early wake to WAIT.
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*
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* It was considered to have an extra state for that
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* trylock, but that would just add more conditionals
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* all over the place for a dubious value.
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*/
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if (old != Q_REQUEUE_PI_NONE)
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break;
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new = Q_REQUEUE_PI_IN_PROGRESS;
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} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
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q->pi_state = pi_state;
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return true;
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}
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static inline void futex_requeue_pi_complete(struct futex_q *q, int locked)
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{
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int old, new;
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old = atomic_read_acquire(&q->requeue_state);
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do {
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if (old == Q_REQUEUE_PI_IGNORE)
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return;
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if (locked >= 0) {
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/* Requeue succeeded. Set DONE or LOCKED */
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WARN_ON_ONCE(old != Q_REQUEUE_PI_IN_PROGRESS &&
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old != Q_REQUEUE_PI_WAIT);
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new = Q_REQUEUE_PI_DONE + locked;
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} else if (old == Q_REQUEUE_PI_IN_PROGRESS) {
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/* Deadlock, no early wakeup interleave */
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new = Q_REQUEUE_PI_NONE;
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} else {
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/* Deadlock, early wakeup interleave. */
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WARN_ON_ONCE(old != Q_REQUEUE_PI_WAIT);
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new = Q_REQUEUE_PI_IGNORE;
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}
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} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
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#ifdef CONFIG_PREEMPT_RT
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/* If the waiter interleaved with the requeue let it know */
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if (unlikely(old == Q_REQUEUE_PI_WAIT))
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rcuwait_wake_up(&q->requeue_wait);
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#endif
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}
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static inline int futex_requeue_pi_wakeup_sync(struct futex_q *q)
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{
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int old, new;
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old = atomic_read_acquire(&q->requeue_state);
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do {
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/* Is requeue done already? */
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if (old >= Q_REQUEUE_PI_DONE)
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return old;
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/*
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* If not done, then tell the requeue code to either ignore
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* the waiter or to wake it up once the requeue is done.
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*/
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new = Q_REQUEUE_PI_WAIT;
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if (old == Q_REQUEUE_PI_NONE)
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new = Q_REQUEUE_PI_IGNORE;
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} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
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/* If the requeue was in progress, wait for it to complete */
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if (old == Q_REQUEUE_PI_IN_PROGRESS) {
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#ifdef CONFIG_PREEMPT_RT
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rcuwait_wait_event(&q->requeue_wait,
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atomic_read(&q->requeue_state) != Q_REQUEUE_PI_WAIT,
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TASK_UNINTERRUPTIBLE);
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#else
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(void)atomic_cond_read_relaxed(&q->requeue_state, VAL != Q_REQUEUE_PI_WAIT);
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#endif
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}
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/*
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* Requeue is now either prohibited or complete. Reread state
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* because during the wait above it might have changed. Nothing
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* will modify q->requeue_state after this point.
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*/
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return atomic_read(&q->requeue_state);
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}
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/**
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* requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
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* @q: the futex_q
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* @key: the key of the requeue target futex
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* @hb: the hash_bucket of the requeue target futex
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*
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* During futex_requeue, with requeue_pi=1, it is possible to acquire the
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* target futex if it is uncontended or via a lock steal.
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*
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* 1) Set @q::key to the requeue target futex key so the waiter can detect
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* the wakeup on the right futex.
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*
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* 2) Dequeue @q from the hash bucket.
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*
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* 3) Set @q::rt_waiter to NULL so the woken up task can detect atomic lock
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* acquisition.
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*
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* 4) Set the q->lock_ptr to the requeue target hb->lock for the case that
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* the waiter has to fixup the pi state.
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*
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* 5) Complete the requeue state so the waiter can make progress. After
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* this point the waiter task can return from the syscall immediately in
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* case that the pi state does not have to be fixed up.
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*
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* 6) Wake the waiter task.
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*
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* Must be called with both q->lock_ptr and hb->lock held.
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*/
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static inline
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void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
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struct futex_hash_bucket *hb)
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{
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q->key = *key;
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__futex_unqueue(q);
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WARN_ON(!q->rt_waiter);
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q->rt_waiter = NULL;
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q->lock_ptr = &hb->lock;
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/* Signal locked state to the waiter */
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futex_requeue_pi_complete(q, 1);
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wake_up_state(q->task, TASK_NORMAL);
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}
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/**
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* futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
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* @pifutex: the user address of the to futex
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* @hb1: the from futex hash bucket, must be locked by the caller
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* @hb2: the to futex hash bucket, must be locked by the caller
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* @key1: the from futex key
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* @key2: the to futex key
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* @ps: address to store the pi_state pointer
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* @exiting: Pointer to store the task pointer of the owner task
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* which is in the middle of exiting
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* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
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*
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* Try and get the lock on behalf of the top waiter if we can do it atomically.
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* Wake the top waiter if we succeed. If the caller specified set_waiters,
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* then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
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* hb1 and hb2 must be held by the caller.
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*
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* @exiting is only set when the return value is -EBUSY. If so, this holds
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* a refcount on the exiting task on return and the caller needs to drop it
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* after waiting for the exit to complete.
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*
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* Return:
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* - 0 - failed to acquire the lock atomically;
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* - >0 - acquired the lock, return value is vpid of the top_waiter
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* - <0 - error
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*/
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static int
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futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
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struct futex_hash_bucket *hb2, union futex_key *key1,
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union futex_key *key2, struct futex_pi_state **ps,
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struct task_struct **exiting, int set_waiters)
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{
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struct futex_q *top_waiter = NULL;
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u32 curval;
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int ret;
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if (futex_get_value_locked(&curval, pifutex))
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return -EFAULT;
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if (unlikely(should_fail_futex(true)))
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return -EFAULT;
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/*
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* Find the top_waiter and determine if there are additional waiters.
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* If the caller intends to requeue more than 1 waiter to pifutex,
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* force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
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* as we have means to handle the possible fault. If not, don't set
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* the bit unnecessarily as it will force the subsequent unlock to enter
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* the kernel.
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*/
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top_waiter = futex_top_waiter(hb1, key1);
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/* There are no waiters, nothing for us to do. */
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if (!top_waiter)
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return 0;
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/*
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* Ensure that this is a waiter sitting in futex_wait_requeue_pi()
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* and waiting on the 'waitqueue' futex which is always !PI.
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*/
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if (!top_waiter->rt_waiter || top_waiter->pi_state)
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return -EINVAL;
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/* Ensure we requeue to the expected futex. */
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if (!futex_match(top_waiter->requeue_pi_key, key2))
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return -EINVAL;
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/* Ensure that this does not race against an early wakeup */
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if (!futex_requeue_pi_prepare(top_waiter, NULL))
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return -EAGAIN;
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/*
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* Try to take the lock for top_waiter and set the FUTEX_WAITERS bit
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* in the contended case or if @set_waiters is true.
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*
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* In the contended case PI state is attached to the lock owner. If
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* the user space lock can be acquired then PI state is attached to
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* the new owner (@top_waiter->task) when @set_waiters is true.
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*/
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ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
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exiting, set_waiters);
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if (ret == 1) {
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/*
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* Lock was acquired in user space and PI state was
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* attached to @top_waiter->task. That means state is fully
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* consistent and the waiter can return to user space
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* immediately after the wakeup.
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*/
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requeue_pi_wake_futex(top_waiter, key2, hb2);
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} else if (ret < 0) {
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/* Rewind top_waiter::requeue_state */
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futex_requeue_pi_complete(top_waiter, ret);
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} else {
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/*
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* futex_lock_pi_atomic() did not acquire the user space
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* futex, but managed to establish the proxy lock and pi
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* state. top_waiter::requeue_state cannot be fixed up here
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* because the waiter is not enqueued on the rtmutex
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* yet. This is handled at the callsite depending on the
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* result of rt_mutex_start_proxy_lock() which is
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* guaranteed to be reached with this function returning 0.
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*/
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}
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return ret;
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}
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/**
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* futex_requeue() - Requeue waiters from uaddr1 to uaddr2
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* @uaddr1: source futex user address
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* @flags: futex flags (FLAGS_SHARED, etc.)
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* @uaddr2: target futex user address
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* @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
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* @nr_requeue: number of waiters to requeue (0-INT_MAX)
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* @cmpval: @uaddr1 expected value (or %NULL)
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* @requeue_pi: if we are attempting to requeue from a non-pi futex to a
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* pi futex (pi to pi requeue is not supported)
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*
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* Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
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* uaddr2 atomically on behalf of the top waiter.
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*
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* Return:
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* - >=0 - on success, the number of tasks requeued or woken;
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* - <0 - on error
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*/
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int futex_requeue(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
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int nr_wake, int nr_requeue, u32 *cmpval, int requeue_pi)
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{
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union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
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int task_count = 0, ret;
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struct futex_pi_state *pi_state = NULL;
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struct futex_hash_bucket *hb1, *hb2;
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struct futex_q *this, *next;
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DEFINE_WAKE_Q(wake_q);
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if (nr_wake < 0 || nr_requeue < 0)
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return -EINVAL;
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/*
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* When PI not supported: return -ENOSYS if requeue_pi is true,
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* consequently the compiler knows requeue_pi is always false past
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* this point which will optimize away all the conditional code
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* further down.
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*/
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if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
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return -ENOSYS;
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if (requeue_pi) {
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/*
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* Requeue PI only works on two distinct uaddrs. This
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* check is only valid for private futexes. See below.
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*/
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if (uaddr1 == uaddr2)
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return -EINVAL;
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/*
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* futex_requeue() allows the caller to define the number
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* of waiters to wake up via the @nr_wake argument. With
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* REQUEUE_PI, waking up more than one waiter is creating
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* more problems than it solves. Waking up a waiter makes
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* only sense if the PI futex @uaddr2 is uncontended as
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* this allows the requeue code to acquire the futex
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* @uaddr2 before waking the waiter. The waiter can then
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* return to user space without further action. A secondary
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* wakeup would just make the futex_wait_requeue_pi()
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* handling more complex, because that code would have to
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* look up pi_state and do more or less all the handling
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* which the requeue code has to do for the to be requeued
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* waiters. So restrict the number of waiters to wake to
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* one, and only wake it up when the PI futex is
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* uncontended. Otherwise requeue it and let the unlock of
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* the PI futex handle the wakeup.
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*
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* All REQUEUE_PI users, e.g. pthread_cond_signal() and
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* pthread_cond_broadcast() must use nr_wake=1.
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*/
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if (nr_wake != 1)
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return -EINVAL;
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/*
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* requeue_pi requires a pi_state, try to allocate it now
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* without any locks in case it fails.
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*/
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if (refill_pi_state_cache())
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return -ENOMEM;
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}
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retry:
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ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
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if (unlikely(ret != 0))
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return ret;
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ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
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requeue_pi ? FUTEX_WRITE : FUTEX_READ);
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if (unlikely(ret != 0))
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return ret;
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/*
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* The check above which compares uaddrs is not sufficient for
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* shared futexes. We need to compare the keys:
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*/
|
|
if (requeue_pi && futex_match(&key1, &key2))
|
|
return -EINVAL;
|
|
|
|
hb1 = futex_hash(&key1);
|
|
hb2 = futex_hash(&key2);
|
|
|
|
retry_private:
|
|
futex_hb_waiters_inc(hb2);
|
|
double_lock_hb(hb1, hb2);
|
|
|
|
if (likely(cmpval != NULL)) {
|
|
u32 curval;
|
|
|
|
ret = futex_get_value_locked(&curval, uaddr1);
|
|
|
|
if (unlikely(ret)) {
|
|
double_unlock_hb(hb1, hb2);
|
|
futex_hb_waiters_dec(hb2);
|
|
|
|
ret = get_user(curval, uaddr1);
|
|
if (ret)
|
|
return ret;
|
|
|
|
if (!(flags & FLAGS_SHARED))
|
|
goto retry_private;
|
|
|
|
goto retry;
|
|
}
|
|
if (curval != *cmpval) {
|
|
ret = -EAGAIN;
|
|
goto out_unlock;
|
|
}
|
|
}
|
|
|
|
if (requeue_pi) {
|
|
struct task_struct *exiting = NULL;
|
|
|
|
/*
|
|
* Attempt to acquire uaddr2 and wake the top waiter. If we
|
|
* intend to requeue waiters, force setting the FUTEX_WAITERS
|
|
* bit. We force this here where we are able to easily handle
|
|
* faults rather in the requeue loop below.
|
|
*
|
|
* Updates topwaiter::requeue_state if a top waiter exists.
|
|
*/
|
|
ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
|
|
&key2, &pi_state,
|
|
&exiting, nr_requeue);
|
|
|
|
/*
|
|
* At this point the top_waiter has either taken uaddr2 or
|
|
* is waiting on it. In both cases pi_state has been
|
|
* established and an initial refcount on it. In case of an
|
|
* error there's nothing.
|
|
*
|
|
* The top waiter's requeue_state is up to date:
|
|
*
|
|
* - If the lock was acquired atomically (ret == 1), then
|
|
* the state is Q_REQUEUE_PI_LOCKED.
|
|
*
|
|
* The top waiter has been dequeued and woken up and can
|
|
* return to user space immediately. The kernel/user
|
|
* space state is consistent. In case that there must be
|
|
* more waiters requeued the WAITERS bit in the user
|
|
* space futex is set so the top waiter task has to go
|
|
* into the syscall slowpath to unlock the futex. This
|
|
* will block until this requeue operation has been
|
|
* completed and the hash bucket locks have been
|
|
* dropped.
|
|
*
|
|
* - If the trylock failed with an error (ret < 0) then
|
|
* the state is either Q_REQUEUE_PI_NONE, i.e. "nothing
|
|
* happened", or Q_REQUEUE_PI_IGNORE when there was an
|
|
* interleaved early wakeup.
|
|
*
|
|
* - If the trylock did not succeed (ret == 0) then the
|
|
* state is either Q_REQUEUE_PI_IN_PROGRESS or
|
|
* Q_REQUEUE_PI_WAIT if an early wakeup interleaved.
|
|
* This will be cleaned up in the loop below, which
|
|
* cannot fail because futex_proxy_trylock_atomic() did
|
|
* the same sanity checks for requeue_pi as the loop
|
|
* below does.
|
|
*/
|
|
switch (ret) {
|
|
case 0:
|
|
/* We hold a reference on the pi state. */
|
|
break;
|
|
|
|
case 1:
|
|
/*
|
|
* futex_proxy_trylock_atomic() acquired the user space
|
|
* futex. Adjust task_count.
|
|
*/
|
|
task_count++;
|
|
ret = 0;
|
|
break;
|
|
|
|
/*
|
|
* If the above failed, then pi_state is NULL and
|
|
* waiter::requeue_state is correct.
|
|
*/
|
|
case -EFAULT:
|
|
double_unlock_hb(hb1, hb2);
|
|
futex_hb_waiters_dec(hb2);
|
|
ret = fault_in_user_writeable(uaddr2);
|
|
if (!ret)
|
|
goto retry;
|
|
return ret;
|
|
case -EBUSY:
|
|
case -EAGAIN:
|
|
/*
|
|
* Two reasons for this:
|
|
* - EBUSY: Owner is exiting and we just wait for the
|
|
* exit to complete.
|
|
* - EAGAIN: The user space value changed.
|
|
*/
|
|
double_unlock_hb(hb1, hb2);
|
|
futex_hb_waiters_dec(hb2);
|
|
/*
|
|
* Handle the case where the owner is in the middle of
|
|
* exiting. Wait for the exit to complete otherwise
|
|
* this task might loop forever, aka. live lock.
|
|
*/
|
|
wait_for_owner_exiting(ret, exiting);
|
|
cond_resched();
|
|
goto retry;
|
|
default:
|
|
goto out_unlock;
|
|
}
|
|
}
|
|
|
|
plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
|
if (task_count - nr_wake >= nr_requeue)
|
|
break;
|
|
|
|
if (!futex_match(&this->key, &key1))
|
|
continue;
|
|
|
|
/*
|
|
* FUTEX_WAIT_REQUEUE_PI and FUTEX_CMP_REQUEUE_PI should always
|
|
* be paired with each other and no other futex ops.
|
|
*
|
|
* We should never be requeueing a futex_q with a pi_state,
|
|
* which is awaiting a futex_unlock_pi().
|
|
*/
|
|
if ((requeue_pi && !this->rt_waiter) ||
|
|
(!requeue_pi && this->rt_waiter) ||
|
|
this->pi_state) {
|
|
ret = -EINVAL;
|
|
break;
|
|
}
|
|
|
|
/* Plain futexes just wake or requeue and are done */
|
|
if (!requeue_pi) {
|
|
if (++task_count <= nr_wake)
|
|
futex_wake_mark(&wake_q, this);
|
|
else
|
|
requeue_futex(this, hb1, hb2, &key2);
|
|
continue;
|
|
}
|
|
|
|
/* Ensure we requeue to the expected futex for requeue_pi. */
|
|
if (!futex_match(this->requeue_pi_key, &key2)) {
|
|
ret = -EINVAL;
|
|
break;
|
|
}
|
|
|
|
/*
|
|
* Requeue nr_requeue waiters and possibly one more in the case
|
|
* of requeue_pi if we couldn't acquire the lock atomically.
|
|
*
|
|
* Prepare the waiter to take the rt_mutex. Take a refcount
|
|
* on the pi_state and store the pointer in the futex_q
|
|
* object of the waiter.
|
|
*/
|
|
get_pi_state(pi_state);
|
|
|
|
/* Don't requeue when the waiter is already on the way out. */
|
|
if (!futex_requeue_pi_prepare(this, pi_state)) {
|
|
/*
|
|
* Early woken waiter signaled that it is on the
|
|
* way out. Drop the pi_state reference and try the
|
|
* next waiter. @this->pi_state is still NULL.
|
|
*/
|
|
put_pi_state(pi_state);
|
|
continue;
|
|
}
|
|
|
|
ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
|
|
this->rt_waiter,
|
|
this->task);
|
|
|
|
if (ret == 1) {
|
|
/*
|
|
* We got the lock. We do neither drop the refcount
|
|
* on pi_state nor clear this->pi_state because the
|
|
* waiter needs the pi_state for cleaning up the
|
|
* user space value. It will drop the refcount
|
|
* after doing so. this::requeue_state is updated
|
|
* in the wakeup as well.
|
|
*/
|
|
requeue_pi_wake_futex(this, &key2, hb2);
|
|
task_count++;
|
|
} else if (!ret) {
|
|
/* Waiter is queued, move it to hb2 */
|
|
requeue_futex(this, hb1, hb2, &key2);
|
|
futex_requeue_pi_complete(this, 0);
|
|
task_count++;
|
|
} else {
|
|
/*
|
|
* rt_mutex_start_proxy_lock() detected a potential
|
|
* deadlock when we tried to queue that waiter.
|
|
* Drop the pi_state reference which we took above
|
|
* and remove the pointer to the state from the
|
|
* waiters futex_q object.
|
|
*/
|
|
this->pi_state = NULL;
|
|
put_pi_state(pi_state);
|
|
futex_requeue_pi_complete(this, ret);
|
|
/*
|
|
* We stop queueing more waiters and let user space
|
|
* deal with the mess.
|
|
*/
|
|
break;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* We took an extra initial reference to the pi_state in
|
|
* futex_proxy_trylock_atomic(). We need to drop it here again.
|
|
*/
|
|
put_pi_state(pi_state);
|
|
|
|
out_unlock:
|
|
double_unlock_hb(hb1, hb2);
|
|
wake_up_q(&wake_q);
|
|
futex_hb_waiters_dec(hb2);
|
|
return ret ? ret : task_count;
|
|
}
|
|
|
|
/**
|
|
* handle_early_requeue_pi_wakeup() - Handle early wakeup on the initial futex
|
|
* @hb: the hash_bucket futex_q was original enqueued on
|
|
* @q: the futex_q woken while waiting to be requeued
|
|
* @timeout: the timeout associated with the wait (NULL if none)
|
|
*
|
|
* Determine the cause for the early wakeup.
|
|
*
|
|
* Return:
|
|
* -EWOULDBLOCK or -ETIMEDOUT or -ERESTARTNOINTR
|
|
*/
|
|
static inline
|
|
int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
|
|
struct futex_q *q,
|
|
struct hrtimer_sleeper *timeout)
|
|
{
|
|
int ret;
|
|
|
|
/*
|
|
* With the hb lock held, we avoid races while we process the wakeup.
|
|
* We only need to hold hb (and not hb2) to ensure atomicity as the
|
|
* wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
|
|
* It can't be requeued from uaddr2 to something else since we don't
|
|
* support a PI aware source futex for requeue.
|
|
*/
|
|
WARN_ON_ONCE(&hb->lock != q->lock_ptr);
|
|
|
|
/*
|
|
* We were woken prior to requeue by a timeout or a signal.
|
|
* Unqueue the futex_q and determine which it was.
|
|
*/
|
|
plist_del(&q->list, &hb->chain);
|
|
futex_hb_waiters_dec(hb);
|
|
|
|
/* Handle spurious wakeups gracefully */
|
|
ret = -EWOULDBLOCK;
|
|
if (timeout && !timeout->task)
|
|
ret = -ETIMEDOUT;
|
|
else if (signal_pending(current))
|
|
ret = -ERESTARTNOINTR;
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
|
|
* @uaddr: the futex we initially wait on (non-pi)
|
|
* @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
|
|
* the same type, no requeueing from private to shared, etc.
|
|
* @val: the expected value of uaddr
|
|
* @abs_time: absolute timeout
|
|
* @bitset: 32 bit wakeup bitset set by userspace, defaults to all
|
|
* @uaddr2: the pi futex we will take prior to returning to user-space
|
|
*
|
|
* The caller will wait on uaddr and will be requeued by futex_requeue() to
|
|
* uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
|
|
* on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
|
|
* userspace. This ensures the rt_mutex maintains an owner when it has waiters;
|
|
* without one, the pi logic would not know which task to boost/deboost, if
|
|
* there was a need to.
|
|
*
|
|
* We call schedule in futex_wait_queue() when we enqueue and return there
|
|
* via the following--
|
|
* 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
|
|
* 2) wakeup on uaddr2 after a requeue
|
|
* 3) signal
|
|
* 4) timeout
|
|
*
|
|
* If 3, cleanup and return -ERESTARTNOINTR.
|
|
*
|
|
* If 2, we may then block on trying to take the rt_mutex and return via:
|
|
* 5) successful lock
|
|
* 6) signal
|
|
* 7) timeout
|
|
* 8) other lock acquisition failure
|
|
*
|
|
* If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
|
|
*
|
|
* If 4 or 7, we cleanup and return with -ETIMEDOUT.
|
|
*
|
|
* Return:
|
|
* - 0 - On success;
|
|
* - <0 - On error
|
|
*/
|
|
int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
|
|
u32 val, ktime_t *abs_time, u32 bitset,
|
|
u32 __user *uaddr2)
|
|
{
|
|
struct hrtimer_sleeper timeout, *to;
|
|
struct rt_mutex_waiter rt_waiter;
|
|
struct futex_hash_bucket *hb;
|
|
union futex_key key2 = FUTEX_KEY_INIT;
|
|
struct futex_q q = futex_q_init;
|
|
struct rt_mutex_base *pi_mutex;
|
|
int res, ret;
|
|
|
|
if (!IS_ENABLED(CONFIG_FUTEX_PI))
|
|
return -ENOSYS;
|
|
|
|
if (uaddr == uaddr2)
|
|
return -EINVAL;
|
|
|
|
if (!bitset)
|
|
return -EINVAL;
|
|
|
|
to = futex_setup_timer(abs_time, &timeout, flags,
|
|
current->timer_slack_ns);
|
|
|
|
/*
|
|
* The waiter is allocated on our stack, manipulated by the requeue
|
|
* code while we sleep on uaddr.
|
|
*/
|
|
rt_mutex_init_waiter(&rt_waiter);
|
|
|
|
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
|
|
q.bitset = bitset;
|
|
q.rt_waiter = &rt_waiter;
|
|
q.requeue_pi_key = &key2;
|
|
|
|
/*
|
|
* Prepare to wait on uaddr. On success, it holds hb->lock and q
|
|
* is initialized.
|
|
*/
|
|
ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
|
if (ret)
|
|
goto out;
|
|
|
|
/*
|
|
* The check above which compares uaddrs is not sufficient for
|
|
* shared futexes. We need to compare the keys:
|
|
*/
|
|
if (futex_match(&q.key, &key2)) {
|
|
futex_q_unlock(hb);
|
|
ret = -EINVAL;
|
|
goto out;
|
|
}
|
|
|
|
/* Queue the futex_q, drop the hb lock, wait for wakeup. */
|
|
futex_wait_queue(hb, &q, to);
|
|
|
|
switch (futex_requeue_pi_wakeup_sync(&q)) {
|
|
case Q_REQUEUE_PI_IGNORE:
|
|
/* The waiter is still on uaddr1 */
|
|
spin_lock(&hb->lock);
|
|
ret = handle_early_requeue_pi_wakeup(hb, &q, to);
|
|
spin_unlock(&hb->lock);
|
|
break;
|
|
|
|
case Q_REQUEUE_PI_LOCKED:
|
|
/* The requeue acquired the lock */
|
|
if (q.pi_state && (q.pi_state->owner != current)) {
|
|
spin_lock(q.lock_ptr);
|
|
ret = fixup_pi_owner(uaddr2, &q, true);
|
|
/*
|
|
* Drop the reference to the pi state which the
|
|
* requeue_pi() code acquired for us.
|
|
*/
|
|
put_pi_state(q.pi_state);
|
|
spin_unlock(q.lock_ptr);
|
|
/*
|
|
* Adjust the return value. It's either -EFAULT or
|
|
* success (1) but the caller expects 0 for success.
|
|
*/
|
|
ret = ret < 0 ? ret : 0;
|
|
}
|
|
break;
|
|
|
|
case Q_REQUEUE_PI_DONE:
|
|
/* Requeue completed. Current is 'pi_blocked_on' the rtmutex */
|
|
pi_mutex = &q.pi_state->pi_mutex;
|
|
ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
|
|
|
|
/* Current is not longer pi_blocked_on */
|
|
spin_lock(q.lock_ptr);
|
|
if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
|
|
ret = 0;
|
|
|
|
debug_rt_mutex_free_waiter(&rt_waiter);
|
|
/*
|
|
* Fixup the pi_state owner and possibly acquire the lock if we
|
|
* haven't already.
|
|
*/
|
|
res = fixup_pi_owner(uaddr2, &q, !ret);
|
|
/*
|
|
* If fixup_pi_owner() returned an error, propagate that. If it
|
|
* acquired the lock, clear -ETIMEDOUT or -EINTR.
|
|
*/
|
|
if (res)
|
|
ret = (res < 0) ? res : 0;
|
|
|
|
futex_unqueue_pi(&q);
|
|
spin_unlock(q.lock_ptr);
|
|
|
|
if (ret == -EINTR) {
|
|
/*
|
|
* We've already been requeued, but cannot restart
|
|
* by calling futex_lock_pi() directly. We could
|
|
* restart this syscall, but it would detect that
|
|
* the user space "val" changed and return
|
|
* -EWOULDBLOCK. Save the overhead of the restart
|
|
* and return -EWOULDBLOCK directly.
|
|
*/
|
|
ret = -EWOULDBLOCK;
|
|
}
|
|
break;
|
|
default:
|
|
BUG();
|
|
}
|
|
|
|
out:
|
|
if (to) {
|
|
hrtimer_cancel(&to->timer);
|
|
destroy_hrtimer_on_stack(&to->timer);
|
|
}
|
|
return ret;
|
|
}
|
|
|