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locking/rtmutex: Clean ->pi_blocked_on in the error case 

The function rt_mutex_wait_proxy_lock() cleans ->pi_blocked_on in case
of failure (timeout, signal). The same cleanup is required in
__rt_mutex_start_proxy_lock().
In both the cases the tasks was interrupted by a signal or timeout while
acquiring the lock and after the interruption it longer blocks on the
lock.

Fixes: 1a1fb985f2 ("futex: Handle early deadlock return correctly")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
This commit is contained in:
Peter Zijlstra 2019-09-30 18:15:44 +02:00 committed by Alibek Omarov
parent 44f08144d7
commit 749c611945
1 changed files with 25 additions and 18 deletions
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43
kernel/locking/rtmutex.c
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@ -2136,6 +2136,26 @@ void rt_mutex_proxy_unlock(struct rt_mutex *lock)
rt_mutex_set_owner(lock, NULL);
}
static void fixup_rt_mutex_blocked(struct rt_mutex *lock)
{
struct task_struct *tsk = current;
/*
* RT has a problem here when the wait got interrupted by a timeout
* or a signal. task->pi_blocked_on is still set. The task must
* acquire the hash bucket lock when returning from this function.
*
* If the hash bucket lock is contended then the
* BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
* task_blocks_on_rt_mutex() will trigger. This can be avoided by
* clearing task->pi_blocked_on which removes the task from the
* boosting chain of the rtmutex. That's correct because the task
* is not longer blocked on it.
*/
raw_spin_lock(&tsk->pi_lock);
tsk->pi_blocked_on = NULL;
raw_spin_unlock(&tsk->pi_lock);
}
/**
* __rt_mutex_start_proxy_lock() - Start lock acquisition for another task
* @lock: the rt_mutex to take
@ -2208,6 +2228,9 @@ int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
ret = 0;
}
if (ret)
fixup_rt_mutex_blocked(lock);
debug_rt_mutex_print_deadlock(waiter);
return ret;
@ -2288,7 +2311,6 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
struct hrtimer_sleeper *to,
struct rt_mutex_waiter *waiter)
{
struct task_struct *tsk = current;
int ret;
raw_spin_lock_irq(&lock->wait_lock);
@ -2300,23 +2322,8 @@ int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
* have to fix that up.
*/
fixup_rt_mutex_waiters(lock);
/*
* RT has a problem here when the wait got interrupted by a timeout
* or a signal. task->pi_blocked_on is still set. The task must
* acquire the hash bucket lock when returning from this function.
*
* If the hash bucket lock is contended then the
* BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
* task_blocks_on_rt_mutex() will trigger. This can be avoided by
* clearing task->pi_blocked_on which removes the task from the
* boosting chain of the rtmutex. That's correct because the task
* is not longer blocked on it.
*/
if (ret) {
raw_spin_lock(&tsk->pi_lock);
tsk->pi_blocked_on = NULL;
raw_spin_unlock(&tsk->pi_lock);
}
if (ret)
fixup_rt_mutex_blocked(lock);
raw_spin_unlock_irq(&lock->wait_lock);