[PATCH] signal: avoid clearing TIF_SIGPENDING in recalc_sigpending() if unset

[Mateusz Guzik <mjguzik@gmail.com>]

Clearing is an atomic op and the flag is not set most of the time.

When creating and destroying threads in the same process with the
pthread family, the primary bottleneck is calls to sigprocmask which
take the process-wide sighand lock.

Avoiding the atomic gives me a 2% bump in start/teardown rate at 24-core
scale.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
---
 kernel/signal.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 081f19a24506..4727b108d842 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -176,9 +176,10 @@ static bool recalc_sigpending_tsk(struct task_struct *t)
 
 void recalc_sigpending(void)
 {
-	if (!recalc_sigpending_tsk(current) && !freezing(current))
-		clear_thread_flag(TIF_SIGPENDING);
-
+	if (!recalc_sigpending_tsk(current) && !freezing(current)) {
+		if (test_thread_flag(TIF_SIGPENDING))
+			clear_thread_flag(TIF_SIGPENDING);
+	}
 }
 EXPORT_SYMBOL(recalc_sigpending);
 
-- 
2.43.0