From: Frederic Weisbecker <frederic@kernel.org>
Date: Mon, 26 Jul 2021 12:55:10 +0000 (+0200)
Subject: posix-cpu-timers: Force next expiration recalc after itimer reset
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=13ccaef77ee86047033c50bf59cb19e0dda3aa97;p=linux-block.git

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

[ 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>
---

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 08c033b80256..d3d42b7637a1 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;
 	}