[PATCH] posix-cpu-timers: don't abuse lock_task_sighand() in handle_posix_cpu_timers()

[Oleg Nesterov <oleg@redhat.com>]

After the commit f90fff1e152d ("posix-cpu-timers: fix race between
handle_posix_cpu_timers() and posix_cpu_timer_del()"), tsk->sighand
is stable in handle_posix_cpu_timers(), so it can use the plain
spin_lock_irqsave(&tsk->sighand->siglock).

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/time/posix-cpu-timers.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index a7d3e8229c4b..d73d31c7994f 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1357,8 +1357,11 @@ static void handle_posix_cpu_timers(struct task_struct *tsk)
 	unsigned long flags, start;
 	LIST_HEAD(firing);
 
-	if (!lock_task_sighand(tsk, &flags))
-		return;
+	/*
+	 * tsk is current and ->sighand is stable, see the
+	 * tsk->exit_state check in run_posix_cpu_timers()
+	 */
+	spin_lock_irqsave(&tsk->sighand->siglock, flags);
 
 	do {
 		/*
@@ -1418,7 +1421,7 @@ static void handle_posix_cpu_timers(struct task_struct *tsk)
 	 * that gets the timer lock before we do will give it up and
 	 * spin until we've taken care of that timer below.
 	 */
-	unlock_task_sighand(tsk, &flags);
+	spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
 
 	/*
 	 * Now that all the timers on our list have the firing flag,
-- 
2.52.0