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| author | Peter Zijlstra <peterz@infradead.org> | 2021-06-30 17:35:18 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-09-22 11:47:48 +0200 |
| commit | b7a041073f4e72083dcd688a003a59bf9d9c9124 (patch) | |
| tree | 6573768d0f44197457d15a974c80ef8c8b28d1f5 | |
| parent | 777631932f4a5185c18b3df1b47f365dbaa70252 (diff) | |
| download | linux-stable-b7a041073f4e72083dcd688a003a59bf9d9c9124.tar.gz linux-stable-b7a041073f4e72083dcd688a003a59bf9d9c9124.tar.bz2 linux-stable-b7a041073f4e72083dcd688a003a59bf9d9c9124.zip | |
locking/mutex: Fix HANDOFF condition
[ Upstream commit 048661a1f963e9517630f080687d48af79ed784c ]
Yanfei reported that setting HANDOFF should not depend on recomputing
@first, only on @first state. Which would then give:
if (ww_ctx || !first)
first = __mutex_waiter_is_first(lock, &waiter);
if (first)
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
But because 'ww_ctx || !first' is basically 'always' and the test for
first is relatively cheap, omit that first branch entirely.
Reported-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com>
Link: https://lore.kernel.org/r/20210630154114.896786297@infradead.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | kernel/locking/mutex.c | 15 |
1 files changed, 5 insertions, 10 deletions
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 354151fef06a..fbc62d360419 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -911,7 +911,6 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) { struct mutex_waiter waiter; - bool first = false; struct ww_mutex *ww; int ret; @@ -986,6 +985,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, set_current_state(state); for (;;) { + bool first; + /* * Once we hold wait_lock, we're serialized against * mutex_unlock() handing the lock off to us, do a trylock @@ -1014,15 +1015,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, spin_unlock(&lock->wait_lock); schedule_preempt_disabled(); - /* - * ww_mutex needs to always recheck its position since its waiter - * list is not FIFO ordered. - */ - if (ww_ctx || !first) { - first = __mutex_waiter_is_first(lock, &waiter); - if (first) - __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF); - } + first = __mutex_waiter_is_first(lock, &waiter); + if (first) + __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF); set_current_state(state); /* |