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Date: Thu, 2 Oct 2014 14:24:09 -0400
From: Dave Jones <davej@redhat.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: hrtimer deadlock caused by nohz_full
Message-ID: <20141002182409.GA29934@redhat.com>
Mail-Followup-To: Dave Jones <davej@redhat.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>
References: <20140925141425.GA21702@redhat.com>
 <alpine.DEB.2.10.1409251630210.4604@nanos>
 <20140925234657.GB14870@lerouge>
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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 ?

	Dave

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