linux-kernel - [PATCH] posix-cpu-timers: Fix spuriously armed 0-value itimer

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Message-Id: <20210913145332.232023-1-frederic@kernel.org>
Date:   Mon, 13 Sep 2021 16:53:32 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Victor Stinner <vstinner@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] posix-cpu-timers: Fix spuriously armed 0-value itimer

Resetting/stopping an itimer eventually leads to it being reprogrammed
with an actual "0" value. As a result the itimer expires on the next
tick, triggering an unexpected signal.

To fix this, make sure that
struct signal_struct::it[CPUCLOCK_PROF/VIRT]::expires is set to 0 when
setitimer() passes a 0 it_value, indicating that the timer must stop.

Reported-by: Victor Stinner <vstinner@...hat.com>
Fixes: 406dd42bd1ba ("posix-cpu-timers: Force next expiration recalc after itimer reset")
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/time/posix-cpu-timers.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index ee736861b18f..643d412ac623 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1404,7 +1404,8 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clkid,
 			}
 		}
 
-		*newval += now;
+		if (*newval)
+			*newval += now;
 	}
 
 	/*
-- 
2.25.1