[PATCH 5.13 011/300] posix-cpu-timers: Force next expiration recalc after itimer reset

Greg Kroah-Hartman
2021-09-13T13:52:05Z

From: Frederic Weisbecker <frederic@kernel.org>

[ Upstream commit 406dd42bd1ba0c01babf9cde169bb319e52f6147 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/time/posix-cpu-timers.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index aa52fc85dbcb..a9f8d25220b1 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1346,8 +1346,6 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clkid,
}
}

- if (!*newval)
- return;
*newval += now;
}

--
2.30.2