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| author | Peter Zijlstra <peterz@infradead.org> | 2021-06-30 17:35:18 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2021-07-07 13:53:24 +0200 |
| commit | 048661a1f963e9517630f080687d48af79ed784c (patch) | |
| tree | b5850f9221b6f8ff66f79b19645c82a2f02d1124 | |
| parent | locking/mutex: Use try_cmpxchg() (diff) | |
| download | linux-048661a1f963e9517630f080687d48af79ed784c.tar.xz linux-048661a1f963e9517630f080687d48af79ed784c.zip | |
locking/mutex: Fix HANDOFF condition
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
| -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 cab7163f9731..8c3d4993b1e0 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -909,7 +909,6 @@ __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; @@ -988,6 +987,8 @@ __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 @@ -1016,15 +1017,9 @@ __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); /* |