[tip: timers/core] posix-cpu-timers: Force next expiration recalc after itimer reset

From: tip-bot2 for Frederic Weisbecker
Date: Tue Aug 10 2021 - 11:15:49 EST


The following commit has been merged into the timers/core branch of tip:

Commit-ID: 406dd42bd1ba0c01babf9cde169bb319e52f6147
Gitweb: https://git.kernel.org/tip/406dd42bd1ba0c01babf9cde169bb319e52f6147
Author: Frederic Weisbecker <frederic@xxxxxxxxxx>
AuthorDate: Mon, 26 Jul 2021 14:55:10 +02:00
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Tue, 10 Aug 2021 17:09:59 +02:00

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

---
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 61c78b6..5c71322 100644
--- 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;
}