From: Thomas Gleixner <tglx@linutronix.de>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Marco Elver <elver@google.com>,
syzbot <syzbot+3b14b2ed9b3d06dcaa07@syzkaller.appspotmail.com>,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
Anna-Maria Behnsen <anna-maria@linutronix.de>,
Jacob Keller <jacob.e.keller@intel.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: WARNING in timer_wait_running
Date: Fri, 07 Apr 2023 19:47:40 +0200 [thread overview]
Message-ID: <87lej3twhv.ffs@tglx> (raw)
In-Reply-To: <ZDADdMnY0oW2k5BV@lothringen>
On Fri, Apr 07 2023 at 13:50, Frederic Weisbecker wrote:
> On Fri, Apr 07, 2023 at 10:44:22AM +0200, Thomas Gleixner wrote:
>> Now memory came back. The problem with posix CPU timers is that it is
>> not really known to the other side which task is actually doing the
>> expiry. For process wide timers this could be any task in the process.
>>
>> For hrtimers this works because the expiring context is known.
>
> So if posix_cpu_timer_del() were to clear ctmr->pid to NULL and then
> delay put_pid() with RCU, we could retrieve that information without
> holding the timer lock (with appropriate RCU accesses all around).
No, you can't. This only gives you the process, but the expiry might run
on any task of that. To make that work you need a mutex in sighand.
Thanks,
tglx
next prev parent reply other threads:[~2023-04-07 17:47 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-31 17:07 WARNING in timer_wait_running syzbot
2023-04-05 21:07 ` Marco Elver
2023-04-05 22:19 ` Frederic Weisbecker
2023-04-06 19:37 ` Thomas Gleixner
2023-04-07 8:44 ` Thomas Gleixner
2023-04-07 11:50 ` Frederic Weisbecker
2023-04-07 17:47 ` Thomas Gleixner [this message]
2023-04-07 18:36 ` Frederic Weisbecker
2023-04-07 19:27 ` Thomas Gleixner
2023-04-07 21:00 ` Frederic Weisbecker
2023-04-11 14:31 ` Marco Elver
2023-04-17 13:37 ` [PATCH] posix-cpu-timers: Implement the missing timer_wait_running callback Thomas Gleixner
2023-04-17 15:34 ` Sebastian Andrzej Siewior
2023-04-18 6:00 ` Marco Elver
2023-04-18 16:44 ` Frederic Weisbecker
2023-04-19 7:33 ` Thomas Gleixner
2023-04-19 8:33 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2023-04-20 7:51 ` tip-bot2 for Thomas Gleixner
2023-04-21 13:43 ` tip-bot2 for Thomas Gleixner
[not found] ` <20230407134620.1034-1-hdanton@sina.com>
2023-04-07 14:49 ` WARNING in timer_wait_running Frederic Weisbecker
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