From: Stafford Horne <shorne@gmail.com>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Victor Stinner <vstinner@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
GLIBC patches <libc-alpha@sourceware.org>
Subject: Re: [PATCH] posix-cpu-timers: Fix spuriously armed 0-value itimer
Date: Sun, 26 Sep 2021 21:58:35 +0900 [thread overview]
Message-ID: <YVBue6owgaW31Kdz@antec> (raw)
In-Reply-To: <20210913145332.232023-1-frederic@kernel.org>
Hello,
Ccing libc-alpha,
On Mon, Sep 13, 2021 at 04:53:32PM +0200, Frederic Weisbecker wrote:
> 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.
Thanks for this I just tracked down the same issue.
I just wanted to give an FYI in case anyone else notices this.
This was causing gprof (gcc -pg) to fail. I noticed this when running the glibc
test suite, tests: gmon/tst-gmon-static, gmon/tst-gmon
Gprof uses ITIMER_PROF, as per:
- https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/posix/profil.c;h=fbf1184df1ccc6e1d2098f92c7d87fc28f5a8f09;hb=HEAD
I was seeing the extra SIGPROF signal after profil de-registered the timer and
signal handler. The spurious signal causes all profiled programs to be killed
and collect no gprof data.
-Stafford
> 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@redhat.com>
> Fixes: 406dd42bd1ba ("posix-cpu-timers: Force next expiration recalc after itimer reset")
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> Cc: Peter Zijlstra (Intel) <peterz@infradead.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
>
prev parent reply other threads:[~2021-09-26 12:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-13 14:53 [PATCH] posix-cpu-timers: Fix spuriously armed 0-value itimer Frederic Weisbecker
2021-09-23 9:57 ` [tip: timers/urgent] posix-cpu-timers: Prevent " tip-bot2 for Frederic Weisbecker
2021-09-26 12:58 ` Stafford Horne [this message]
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