Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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
+5
-10
+5
-10
kernel/locking/mutex.c
+5
-10
kernel/locking/mutex.c
···
909
909
struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
910
910
{
911
911
struct mutex_waiter waiter;
912
-
bool first = false;
913
912
struct ww_mutex *ww;
914
913
int ret;
915
914
···
987
988
988
989
set_current_state(state);
989
990
for (;;) {
991
+
bool first;
992
+
990
993
/*
991
994
* Once we hold wait_lock, we're serialized against
992
995
* mutex_unlock() handing the lock off to us, do a trylock
···
1017
1016
spin_unlock(&lock->wait_lock);
1018
1017
schedule_preempt_disabled();
1019
1018
1020
-
/*
1021
-
* ww_mutex needs to always recheck its position since its waiter
1022
-
* list is not FIFO ordered.
1023
-
*/
1024
-
if (ww_ctx || !first) {
1025
-
first = __mutex_waiter_is_first(lock, &waiter);
1026
-
if (first)
1027
-
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
1028
-
}
1019
+
first = __mutex_waiter_is_first(lock, &waiter);
1020
+
if (first)
1021
+
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
1029
1022
1030
1023
set_current_state(state);
1031
1024
/*