Commit 7be88aa5 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Sebastian Andrzej Siewior
Browse files

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

Similar to the issues in commits:

  6467822b ("locking/rtmutex: Prevent spurious EDEADLK return caused by ww_mutexes")
  a055fcc1

 ("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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20211129174654.668506-4-bigeasy@linutronix.de
parent d9136b64
......@@ -1103,27 +1103,12 @@ 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 defined(DEBUG_WW_MUTEXES) && defined(CONFIG_DEBUG_LOCKING_API_SELFTESTS)
/*
* The lockdep selftest for ww-mutex assumes in a few cases
* the ww_ctx->contending_lock assignment via
* __ww_mutex_check_kill() which does not happen if the rtmutex
* detects the deadlock early.
*/
if (build_ww_mutex() && ww_ctx) {
struct rt_mutex *rtm;
/* Check whether the waiter should backout immediately */
rtm = container_of(lock, struct rt_mutex, rtmutex);
__ww_mutex_add_waiter(waiter, rtm, ww_ctx);
__ww_mutex_check_kill(rtm, waiter, ww_ctx);
}
#endif
if (owner == task && !(build_ww_mutex() && ww_ctx))
return -EDEADLK;
}
raw_spin_lock(&task->pi_lock);
waiter->task = task;
......
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