From: Peter Zijlstra peterz@infradead.org
[ 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 --- kernel/locking/mutex.c | 15 +++++---------- 1 file 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); /*