posix-cpu-timers: Force next expiration recalc after itimer reset

When an itimer deactivates a previously armed expiration, it simply doesn't
do anything. As a result the process wide cputime counter keeps running and
the tick dependency stays set until it reaches the old ghost expiration
value.

This can be reproduced with the following snippet:

	void trigger_process_counter(void)
	{
		struct itimerval n = {};

		n.it_value.tv_sec = 100;
		setitimer(ITIMER_VIRTUAL, &n, NULL);
		n.it_value.tv_sec = 0;
		setitimer(ITIMER_VIRTUAL, &n, NULL);
	}

Fix this with resetting the relevant base expiration. This is similar to
disarming a timer.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210726125513.271824-4-frederic@kernel.org

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 61c78b62fe6a1c0e64e93b4038fa5f328525c201..5c71322b45c7590bb9142aa63297e4fc4077caaa 100644 (file)
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1379,8 +1379,6 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clkid,
                        }
                }
 
-               if (!*newval)
-                       return;
                *newval += now;
        }