Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fixes from Ingo Molnar: "An rtmutex (PI-futex) deadlock scenario fix, plus a locking documentation fix" * 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: futex: Handle early deadlock return correctly futex: Fix barrier comment
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d2a6aae99f
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@ -2221,11 +2221,11 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
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* decrement the counter at queue_unlock() when some error has
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* occurred and we don't end up adding the task to the list.
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*/
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hb_waiters_inc(hb);
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hb_waiters_inc(hb); /* implies smp_mb(); (A) */
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q->lock_ptr = &hb->lock;
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spin_lock(&hb->lock); /* implies smp_mb(); (A) */
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spin_lock(&hb->lock);
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return hb;
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}
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@ -2861,35 +2861,39 @@ retry_private:
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* and BUG when futex_unlock_pi() interleaves with this.
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*
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* Therefore acquire wait_lock while holding hb->lock, but drop the
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* latter before calling rt_mutex_start_proxy_lock(). This still fully
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* serializes against futex_unlock_pi() as that does the exact same
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* lock handoff sequence.
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* latter before calling __rt_mutex_start_proxy_lock(). This
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* interleaves with futex_unlock_pi() -- which does a similar lock
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* handoff -- such that the latter can observe the futex_q::pi_state
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* before __rt_mutex_start_proxy_lock() is done.
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*/
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raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
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spin_unlock(q.lock_ptr);
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/*
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* __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
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* such that futex_unlock_pi() is guaranteed to observe the waiter when
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* it sees the futex_q::pi_state.
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*/
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ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
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raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
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if (ret) {
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if (ret == 1)
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ret = 0;
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spin_lock(q.lock_ptr);
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goto no_block;
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goto cleanup;
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}
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if (unlikely(to))
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hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS);
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ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
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cleanup:
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spin_lock(q.lock_ptr);
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/*
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* If we failed to acquire the lock (signal/timeout), we must
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* If we failed to acquire the lock (deadlock/signal/timeout), we must
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* first acquire the hb->lock before removing the lock from the
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* rt_mutex waitqueue, such that we can keep the hb and rt_mutex
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* wait lists consistent.
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* rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
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* lists consistent.
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*
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* In particular; it is important that futex_unlock_pi() can not
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* observe this inconsistency.
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@ -3013,6 +3017,10 @@ retry:
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* there is no point where we hold neither; and therefore
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* wake_futex_pi() must observe a state consistent with what we
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* observed.
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*
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* In particular; this forces __rt_mutex_start_proxy() to
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* complete such that we're guaranteed to observe the
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* rt_waiter. Also see the WARN in wake_futex_pi().
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*/
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raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
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spin_unlock(&hb->lock);
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@ -1726,12 +1726,33 @@ void rt_mutex_proxy_unlock(struct rt_mutex *lock,
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rt_mutex_set_owner(lock, NULL);
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}
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/**
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* __rt_mutex_start_proxy_lock() - Start lock acquisition for another task
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* @lock: the rt_mutex to take
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* @waiter: the pre-initialized rt_mutex_waiter
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* @task: the task to prepare
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*
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* Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
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* detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
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*
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* NOTE: does _NOT_ remove the @waiter on failure; must either call
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* rt_mutex_wait_proxy_lock() or rt_mutex_cleanup_proxy_lock() after this.
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*
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* Returns:
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* 0 - task blocked on lock
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* 1 - acquired the lock for task, caller should wake it up
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* <0 - error
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*
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* Special API call for PI-futex support.
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*/
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int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
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struct rt_mutex_waiter *waiter,
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struct task_struct *task)
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{
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int ret;
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lockdep_assert_held(&lock->wait_lock);
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if (try_to_take_rt_mutex(lock, task, NULL))
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return 1;
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@ -1749,9 +1770,6 @@ int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
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ret = 0;
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}
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if (unlikely(ret))
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remove_waiter(lock, waiter);
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debug_rt_mutex_print_deadlock(waiter);
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return ret;
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@ -1763,12 +1781,18 @@ int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
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* @waiter: the pre-initialized rt_mutex_waiter
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* @task: the task to prepare
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*
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* Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
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* detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
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*
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* NOTE: unlike __rt_mutex_start_proxy_lock this _DOES_ remove the @waiter
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* on failure.
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*
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* Returns:
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* 0 - task blocked on lock
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* 1 - acquired the lock for task, caller should wake it up
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* <0 - error
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*
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* Special API call for FUTEX_REQUEUE_PI support.
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* Special API call for PI-futex support.
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*/
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int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
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struct rt_mutex_waiter *waiter,
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@ -1778,6 +1802,8 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
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raw_spin_lock_irq(&lock->wait_lock);
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ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
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if (unlikely(ret))
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remove_waiter(lock, waiter);
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raw_spin_unlock_irq(&lock->wait_lock);
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return ret;
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@ -1845,7 +1871,8 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
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* @lock: the rt_mutex we were woken on
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* @waiter: the pre-initialized rt_mutex_waiter
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*
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* Attempt to clean up after a failed rt_mutex_wait_proxy_lock().
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* Attempt to clean up after a failed __rt_mutex_start_proxy_lock() or
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* rt_mutex_wait_proxy_lock().
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*
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* Unless we acquired the lock; we're still enqueued on the wait-list and can
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* in fact still be granted ownership until we're removed. Therefore we can
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