locking/mutex: Fix HANDOFF condition (a5e42516) · Commits · e / devices / android_kernel_fairphone_FP5

[ 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

+5 −10

Original line number	Diff line number	Diff line
		@@ -938,7 +938,6 @@ __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;

		@@ -1017,6 +1016,8 @@ __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
		@@ -1045,15 +1046,9 @@ __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);
		}

		set_current_state(state);
		/*