posix-cpu-timers: Pass the task into arm_timer()

The task has been already computed to take siglock before calling
arm_timer. So pass the benefit of that labor into arm_timer().
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/8736auvdt1.fsf@x220.int.ebiederm.org

kernel/time/posix-cpu-timers.c

@@ -482,12 +482,11 @@ void posix_cpu_timers_exit_group(struct task_struct *tsk)
  * Insert the timer on the appropriate list before any timers that
  * expire later.  This must be called with the sighand lock held.
  */
-static void arm_timer(struct k_itimer *timer)
+static void arm_timer(struct k_itimer *timer, struct task_struct *p)
 {
 	int clkidx = CPUCLOCK_WHICH(timer->it_clock);
 	struct cpu_timer *ctmr = &timer->it.cpu;
 	u64 newexp = cpu_timer_getexpires(ctmr);
-	struct task_struct *p = ctmr->task;
 	struct posix_cputimer_base *base;
 
 	if (CPUCLOCK_PERTHREAD(timer->it_clock))
@@ -660,7 +659,7 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
 	 */
 	cpu_timer_setexpires(ctmr, new_expires);
 	if (new_expires != 0 && val < new_expires) {
-		arm_timer(timer);
+		arm_timer(timer, p);
 	}
 
 	unlock_task_sighand(p, &flags);
@@ -980,7 +979,7 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer)
 	/*
 	 * Now re-arm for the new expiry time.
 	 */
-	arm_timer(timer);
+	arm_timer(timer, p);
 	unlock_task_sighand(p, &flags);
 }