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Groups > linux.kernel > #1734646
| From | "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: Query regarding synchronize_sched_expedited and resched_cpu |
| Date | 2017-09-19 06:10 +0200 |
| Message-ID | <uri1d-7Do-25@gated-at.bofh.it> (permalink) |
| References | (5 earlier) <ure7g-4Xi-1@gated-at.bofh.it> <urfZn-66X-1@gated-at.bofh.it> <urg94-6pO-3@gated-at.bofh.it> <urgC5-6EL-9@gated-at.bofh.it> <urgLM-6I2-21@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Tue, Sep 19, 2017 at 11:48:22AM +0900, Byungchul Park wrote:
> On Mon, Sep 18, 2017 at 07:33:29PM -0700, Paul E. McKenney wrote:
> > > > Hello Paul and Steven,
> > > >
> > > > This is saying:
> > > >
> > > > Thread A
> > > > --------
> > > > takedown_cpu()
> > > > irq_lock_sparse()
> > > > wait_for_completion(&st->done) // Wait for completion of B
> > > > irq_unlock_sparse()
> > > >
> > > > Thread B
> > > > --------
> > > > cpuhp_invoke_callback()
> > > > irq_lock_sparse() // Wait for A to irq_unlock_sparse()
> > > > (on the way going to complete(&st->done))
> > > >
> > > > So, lockdep consider this as a deadlock.
> > > > Is it possible to happen?
> > >
> > > In addition, if it's impossible, then we should fix lock class
> > > assignments so that the locks actually have different classes.
> >
> > Interesting, and thank you for the analysis!
> >
> > The strange thing is that the way you describe it, this would be a
> > deterministic deadlock. Yet CPU hotplug operations complete just fine
> > in my tests. What am I missing here?
>
> Hi, :)
>
> Lockdep basically reports either (1) an actual deadlock happened at the
> time or (2) a deadlock possibility, even w/o LOCKDEP_CROSSRELEASE.
>
> Both are useful. But LOCKDEP_CROSSRELEASE can only do the latter. IOW,
> the deadlock would actually happen _only_ when the two threads(A and B)
> run simultaniously.
>
> In your case, those two threads might run at different timings. So it's
> not an actual deadlock, but still has a possibility for the problem to
> happen later.
Fair enough, if the wakeup always happened first, deadlock might well
be avoided. If the sleep happened first, I suspect deadlock would
be deterministic in this case.
Thanx, Paul
> > > > Thanks,
> > > > Byungchul
> > > >
> > > > > [ 35.313943]
> > > > > [ 35.313943] 3 locks held by torture_onoff/766:
> > > > > [ 35.313943] #0: (cpu_add_remove_lock){+.+.}, at: [<ffffffffb9060be2>] do_cpu_down+0x22/0x50
> > > > > [ 35.313943] #1: (cpu_hotplug_lock.rw_sem){++++}, at: [<ffffffffb90acc41>] percpu_down_write+0x21/0xf0
> > > > > [ 35.313943] #2: (sparse_irq_lock){+.+.}, at: [<ffffffffb90c5e42>] irq_lock_sparse+0x12/0x20
> > > > > [ 35.313943]
> > > > > [ 35.313943] stack backtrace:
> > > > > [ 35.313943] CPU: 7 PID: 766 Comm: torture_onoff Not tainted 4.13.0-rc4+ #1
> > > > > [ 35.313943] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> > > > > [ 35.313943] Call Trace:
> > > > > [ 35.313943] dump_stack+0x67/0x97
> > > > > [ 35.313943] print_circular_bug+0x21d/0x330
> > > > > [ 35.313943] ? add_lock_to_list.isra.31+0xc0/0xc0
> > > > > [ 35.313943] check_prev_add+0x401/0x800
> > > > > [ 35.313943] ? wake_up_q+0x70/0x70
> > > > > [ 35.313943] __lock_acquire+0x1100/0x11a0
> > > > > [ 35.313943] ? __lock_acquire+0x1100/0x11a0
> > > > > [ 35.313943] ? add_lock_to_list.isra.31+0xc0/0xc0
> > > > > [ 35.313943] lock_acquire+0x9e/0x1e0
> > > > > [ 35.313943] ? takedown_cpu+0x86/0xf0
> > > > > [ 35.313943] wait_for_completion+0x36/0x130
> > > > > [ 35.313943] ? takedown_cpu+0x86/0xf0
> > > > > [ 35.313943] ? stop_machine_cpuslocked+0xb9/0xd0
> > > > > [ 35.313943] ? cpuhp_invoke_callback+0x8b0/0x8b0
> > > > > [ 35.313943] ? cpuhp_complete_idle_dead+0x10/0x10
> > > > > [ 35.313943] takedown_cpu+0x86/0xf0
> > > > > [ 35.313943] cpuhp_invoke_callback+0xa7/0x8b0
> > > > > [ 35.313943] cpuhp_down_callbacks+0x3d/0x80
> > > > > [ 35.313943] _cpu_down+0xbb/0xf0
> > > > > [ 35.313943] do_cpu_down+0x39/0x50
> > > > > [ 35.313943] cpu_down+0xb/0x10
> > > > > [ 35.313943] torture_offline+0x75/0x140
> > > > > [ 35.313943] torture_onoff+0x102/0x1e0
> > > > > [ 35.313943] kthread+0x142/0x180
> > > > > [ 35.313943] ? torture_kthread_stopping+0x70/0x70
> > > > > [ 35.313943] ? kthread_create_on_node+0x40/0x40
> > > > > [ 35.313943] ret_from_fork+0x27/0x40
> > >
>
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Query regarding synchronize_sched_expedited and resched_cpu Neeraj Upadhyay <neeraju@codeaurora.org> - 2017-09-15 13:20 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-17 03:10 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Neeraj Upadhyay <neeraju@codeaurora.org> - 2017-09-17 08:10 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Steven Rostedt <rostedt@goodmis.org> - 2017-09-18 17:20 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-18 18:10 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Steven Rostedt <rostedt@goodmis.org> - 2017-09-18 18:20 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Steven Rostedt <rostedt@goodmis.org> - 2017-09-18 18:30 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-18 19:00 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-19 02:00 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Steven Rostedt <rostedt@goodmis.org> - 2017-09-19 03:30 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-19 04:30 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Byungchul Park <byungchul.park@lge.com> - 2017-09-19 04:00 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Byungchul Park <byungchul.park@lge.com> - 2017-09-19 04:10 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-19 04:40 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Byungchul Park <byungchul.park@lge.com> - 2017-09-19 04:50 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-19 06:10 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Boqun Feng <boqun.feng@gmail.com> - 2017-09-19 07:40 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Mike Galbraith <efault@gmx.de> - 2017-09-19 08:20 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Byungchul Park <byungchul.park@lge.com> - 2017-09-19 09:00 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-19 15:50 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Peter Zijlstra <peterz@infradead.org> - 2017-09-21 16:00 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-21 17:40 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Byungchul Park <byungchul.park@lge.com> - 2017-09-19 04:00 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-18 18:30 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-19 17:40 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Steven Rostedt <rostedt@goodmis.org> - 2017-09-19 18:00 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-19 18:20 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Peter Zijlstra <peterz@infradead.org> - 2017-09-21 16:10 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-21 18:10 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Peter Zijlstra <peterz@infradead.org> - 2017-09-21 18:40 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-21 18:50 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Peter Zijlstra <peterz@infradead.org> - 2017-09-21 16:00 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-09-21 17:40 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Peter Zijlstra <peterz@infradead.org> - 2017-09-21 18:20 +0200
Re: Query regarding synchronize_sched_expedited and resched_cpu Steven Rostedt <rostedt@goodmis.org> - 2017-09-21 17:50 +0200
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