forked from luck/tmp_suning_uos_patched
rtmutex: Fix deadlock detector for real
The current deadlock detection logic does not work reliably due to the following early exit path: /* * Drop out, when the task has no waiters. Note, * top_waiter can be NULL, when we are in the deboosting * mode! */ if (top_waiter && (!task_has_pi_waiters(task) || top_waiter != task_top_pi_waiter(task))) goto out_unlock_pi; So this not only exits when the task has no waiters, it also exits unconditionally when the current waiter is not the top priority waiter of the task. So in a nested locking scenario, it might abort the lock chain walk and therefor miss a potential deadlock. Simple fix: Continue the chain walk, when deadlock detection is enabled. We also avoid the whole enqueue, if we detect the deadlock right away (A-A). It's an optimization, but also prevents that another waiter who comes in after the detection and before the task has undone the damage observes the situation and detects the deadlock and returns -EDEADLOCK, which is wrong as the other task is not in a deadlock situation. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20140522031949.725272460@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
parent
f0d71b3dcb
commit
397335f004
|
@ -343,9 +343,16 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
|
||||||
* top_waiter can be NULL, when we are in the deboosting
|
* top_waiter can be NULL, when we are in the deboosting
|
||||||
* mode!
|
* mode!
|
||||||
*/
|
*/
|
||||||
if (top_waiter && (!task_has_pi_waiters(task) ||
|
if (top_waiter) {
|
||||||
top_waiter != task_top_pi_waiter(task)))
|
if (!task_has_pi_waiters(task))
|
||||||
goto out_unlock_pi;
|
goto out_unlock_pi;
|
||||||
|
/*
|
||||||
|
* If deadlock detection is off, we stop here if we
|
||||||
|
* are not the top pi waiter of the task.
|
||||||
|
*/
|
||||||
|
if (!detect_deadlock && top_waiter != task_top_pi_waiter(task))
|
||||||
|
goto out_unlock_pi;
|
||||||
|
}
|
||||||
|
|
||||||
/*
|
/*
|
||||||
* When deadlock detection is off then we check, if further
|
* When deadlock detection is off then we check, if further
|
||||||
|
@ -361,7 +368,12 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
|
||||||
goto retry;
|
goto retry;
|
||||||
}
|
}
|
||||||
|
|
||||||
/* Deadlock detection */
|
/*
|
||||||
|
* 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) {
|
if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
|
||||||
debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
|
debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
|
||||||
raw_spin_unlock(&lock->wait_lock);
|
raw_spin_unlock(&lock->wait_lock);
|
||||||
|
@ -527,6 +539,18 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
|
||||||
unsigned long flags;
|
unsigned long flags;
|
||||||
int chain_walk = 0, res;
|
int chain_walk = 0, res;
|
||||||
|
|
||||||
|
/*
|
||||||
|
* 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 (detect_deadlock && owner == task)
|
||||||
|
return -EDEADLK;
|
||||||
|
|
||||||
raw_spin_lock_irqsave(&task->pi_lock, flags);
|
raw_spin_lock_irqsave(&task->pi_lock, flags);
|
||||||
__rt_mutex_adjust_prio(task);
|
__rt_mutex_adjust_prio(task);
|
||||||
waiter->task = task;
|
waiter->task = task;
|
||||||
|
|
Loading…
Reference in New Issue
Block a user