linux-kernel - Re: hrtimer deadlock caused by nohz

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Message-ID: <20141007153024.GA14119@lerouge>
Date:	Tue, 7 Oct 2014 17:30:27 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Dave Jones <davej@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: hrtimer deadlock caused by nohz_full

On Thu, Oct 02, 2014 at 02:24:09PM -0400, Dave Jones wrote:
> On Fri, Sep 26, 2014 at 01:46:59AM +0200, Frederic Weisbecker wrote:
> 
>  > > >  [<ffffffffa10f95f8>] hrtimer_try_to_cancel+0x58/0x1f0
>  > > >  [<ffffffffa10f97aa>] hrtimer_cancel+0x1a/0x30
>  > > >  [<ffffffffa110a0e7>] tick_nohz_restart+0x17/0x90
>  > > >  [<ffffffffa110af38>] __tick_nohz_full_check+0xc8/0xe0
>  > > >  [<ffffffffa110af5e>] nohz_full_kick_work_func+0xe/0x10
>  > > >  [<ffffffffa117c9bf>] irq_work_run_list+0x4f/0x70
>  > > >  [<ffffffffa117ca0a>] irq_work_run+0x2a/0x60
>  > > >  [<ffffffffa10f82eb>] update_process_times+0x5b/0x70
>  > > >  [<ffffffffa1109dc5>] tick_sched_handle.isra.21+0x25/0x60
>  > > >  [<ffffffffa110a0b1>] tick_sched_timer+0x41/0x60
>  > > >  [<ffffffffa10f8c71>] __run_hrtimer+0x81/0x480
>  > > >  [<ffffffffa110a070>] ? tick_sched_do_timer+0x90/0x90
>  > > >  [<ffffffffa10f9b27>] hrtimer_interrupt+0x107/0x260
>  > > >  [<ffffffffa10331a4>] local_apic_timer_interrupt+0x34/0x60
>  > > >  [<ffffffffa182734f>] smp_apic_timer_interrupt+0x3f/0x60
>  > > >  [<ffffffffa182576f>] apic_timer_interrupt+0x6f/0x80
>  > > 
>  > > hrtimer_interrupt
>  > >   tick_sched_timer
>  > >     tick_sched_handle
>  > >       update_process_times
>  > >         irq_work_run
>  > > 	  irq_work_run_list
>  > > 	    nohz_full_kick_work_func
>  > > 	      __tick_nohz_full_check
>  > > 	        tick_nohz_restart
>  > >                   hrtimer_cancel
>  > > 
>  > > And that hrtimer_cancel is:
>  > > 
>  > > static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
>  > > {
>  > > 	hrtimer_cancel(&ts->sched_timer);
>  > > 
>  > > Now, that's really bad because we are in the timer callback of
>  > > ts->sched_timer. So hrtimer_cancel will loop forever waiting for the
>  > > callback to complete.
>  > > 
>  > > Frederic !?!?
>  > 
>  > Right, this patchset fixes it: "[PATCH 0/8] nohz: Fix nohz kick irq work on tick v3"
>  > 
>  > I was about to make the pull request, the branch is acked by peterz.
>  > Would you like to pull it? It's all merge window material.
>  > 
>  > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
>  > 	nohz/fixes-v3
> 
> I'm now hitting this with such regularity that it's preventing me from
> tracking down other bugs.  Can we get this merged soon please ?

I asked Thomas to pull but he probably missed it. So I did a formal pull request
to Ingo a few days later but he told me that the pull request was made too late
as the merge window was too close. I told him it fixes annoying bugs but that was on IRC
so this probably got lost.

It will probably be delayed to 3.18
Sorry I don't have much control myself on merging patches upstream.
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