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locking/rtmutex: Squash self-deadlock check for ww_rt_mutex.

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Similar to the issues in commits:

  6467822b8c ("locking/rtmutex: Prevent spurious EDEADLK return caused by ww_mutexes")
  a055fcc132 ("locking/rtmutex: Return success on deadlock for ww_mutex waiters")

ww_rt_mutex_lock() should not return EDEADLK without first going through
the __ww_mutex logic to set the required state. In fact, the chain-walk
can deal with the spurious cycles (per the above commits) this check
warns about and is trying to avoid.

Therefore ignore this test for ww_rt_mutex and simply let things fall
in place.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20211129174654.668506-4-bigeasy@linutronix.de
This commit is contained in:
Peter Zijlstra 2021-11-29 18:46:46 +01:00
parent e08f343be0
commit 02ea9fc96f
1 changed files with 4 additions and 1 deletions
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5
kernel/locking/rtmutex.c
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@ -1103,8 +1103,11 @@ static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
* the other will detect the deadlock and return -EDEADLOCK,
* which is wrong, as the other waiter is not in a deadlock
* situation.
*
* Except for ww_mutex, in that case the chain walk must already deal
* with spurious cycles, see the comments at [3] and [6].
*/
if (owner == task)
if (owner == task && !(build_ww_mutex() && ww_ctx))
return -EDEADLK;
raw_spin_lock(&task->pi_lock);