Messages in this thread Patch in this message | | | Date | Mon, 06 Dec 2021 15:15:48 -0000 | From | "tip-bot2 for Peter Zijlstra" <> | Subject | [tip: locking/core] locking/rtmutex: Squash self-deadlock check for ww_rt_mutex. |
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The following commit has been merged into the locking/core branch of tip:
Commit-ID: 02ea9fc96fe976e7f7e067f38b12202f126e3f2f Gitweb: https://git.kernel.org/tip/02ea9fc96fe976e7f7e067f38b12202f126e3f2f Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Mon, 29 Nov 2021 18:46:46 +01:00 Committer: Peter Zijlstra <peterz@infradead.org> CommitterDate: Sat, 04 Dec 2021 10:56:23 +01:00
locking/rtmutex: Squash self-deadlock check for ww_rt_mutex.
Similar to the issues in commits:
6467822b8cc9 ("locking/rtmutex: Prevent spurious EDEADLK return caused by ww_mutexes") a055fcc132d4 ("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 --- kernel/locking/rtmutex.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 0c6a48d..f896208 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -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);
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