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From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@kernel.org>
Subject: [PATCH 6/6] posix-cpu-timers: Force next expiration recalc after itimer reset
Date: Fri,  4 Jun 2021 13:31:59 +0200	[thread overview]
Message-ID: <20210604113159.26177-7-frederic@kernel.org> (raw)
In-Reply-To: <20210604113159.26177-1-frederic@kernel.org>

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 we reach 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>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
---
 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 d8325a906314..8a1ec78a7ebb 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1407,8 +1407,6 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clkid,
 			}
 		}
 
-		if (!*newval)
-			return;
 		*newval += now;
 	}
 
-- 
2.25.1


      parent reply	other threads:[~2021-06-04 11:32 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-04 11:31 [PATCH 0/6] posix-cpu-timers: Bunch of fixes Frederic Weisbecker
2021-06-04 11:31 ` [PATCH 1/6] posix-cpu-timers: Fix rearm racing against process tick Frederic Weisbecker
2021-06-09 11:54   ` Frederic Weisbecker
2021-06-11 11:49     ` Peter Zijlstra
2021-06-11 12:37       ` Frederic Weisbecker
2021-06-04 11:31 ` [PATCH 2/6] posix-cpu-timers: Don't start process wide cputime counter if timer is disabled Frederic Weisbecker
2021-06-09 12:18   ` Frederic Weisbecker
2021-06-10 10:24     ` Frederic Weisbecker
2021-06-16  8:51   ` Peter Zijlstra
2021-06-16 10:51     ` Frederic Weisbecker
2021-06-16 11:26       ` Peter Zijlstra
2021-06-16 11:50         ` Peter Zijlstra
2021-06-04 11:31 ` [PATCH 3/6] posix-cpu-timers: Force next_expiration recalc after timer deletion Frederic Weisbecker
2021-06-16  9:16   ` Peter Zijlstra
2021-06-04 11:31 ` [PATCH 4/6] posix-cpu-timers: Force next_expiration recalc after timer reset Frederic Weisbecker
2021-06-16  9:23   ` Peter Zijlstra
2021-06-16 11:21     ` Frederic Weisbecker
2021-06-16 11:33       ` Peter Zijlstra
2021-06-04 11:31 ` [PATCH 5/6] posix-cpu-timers: Force next expiration recalc after early timer firing Frederic Weisbecker
2021-06-16  9:42   ` Peter Zijlstra
2021-06-16 11:59     ` Frederic Weisbecker
2021-06-16 13:23       ` Peter Zijlstra
2021-06-16 14:53         ` Frederic Weisbecker
2021-06-04 11:31 ` Frederic Weisbecker [this message]

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