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

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Date:   Tue, 10 Aug 2021 15:13:33 -0000
From:   "tip-bot2 for Frederic Weisbecker" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: timers/core] posix-cpu-timers: Force next expiration recalc
 after itimer reset

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@...nel.org>
AuthorDate:    Mon, 26 Jul 2021 14:55:10 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
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@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20210726125513.271824-4-frederic@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 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;
 	}