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Groups > linux.kernel > #1721703
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: WARNING: possible circular locking dependency detected |
| Date | 2017-08-28 17:00 +0200 |
| Message-ID | <ujtGb-6PN-29@gated-at.bofh.it> (permalink) |
| References | <uijIS-2Ic-11@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Fri, Aug 25, 2017 at 12:03:04PM +0200, Borislav Petkov wrote:
> Hey,
>
> tglx says I have something for ya :-)
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.13.0-rc6+ #1 Not tainted
> ------------------------------------------------------
> watchdog/3/27 is trying to acquire lock:
> (cpu_hotplug_lock.rw_sem){++++}, at: [<ffffffff8100c489>] release_ds_buffers+0x29/0xd0
>
> but now in release context of a crosslock acquired at the following:
> ((complete)&self->parked){+.+.}, at: [<ffffffff810895f6>] kthread_park+0x46/0x60
So I'm thinking this one is an actual deadlock.
So, as far as I can tell this ends up being:
CPU0 CPU1
(smpboot_regiser_percpu_thread_cpumask)
get_online_cpus()
__smpboot_create_thread()
kthread_park();
wait_for_completion(&X)
(smpboot_thread_fn)
->park() := watchdog_disable()
watchdog_nmi_disable()
perf_event_release_kernel();
put_event()
_free_event()
->destroy() := hw_perf_event_destroy()
x86_release_hardware()
release_ds_buffers()
get_online_cpus()
kthread_parkme()
complete(&X)
So CPU0 holds cpus_hotplug_lock while wait_for_completion() and CPU1
needs to acquire before complete().
So if, in between, CPU2 does down_write(), things will get unstuck.
What's worse, there's also:
cpus_write_lock()
...
takedown_cpu()
smpboot_park_threads()
smpboot_park_thread()
kthread_park()
->park() := watchdog_disable()
watchdog_nmi_disable()
perf_event_release_kernel();
put_event()
_free_event()
->destroy() := hw_perf_event_destroy()
x86_release_hardware()
release_ds_buffers()
get_online_cpus()
which as far as I can tell, spells instant deadlock..
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Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-28 17:00 +0200
Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-28 17:10 +0200
Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-28 18:40 +0200
Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-29 19:50 +0200
Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-29 21:50 +0200
Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-29 22:20 +0200
Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-30 07:50 +0200
Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-31 09:10 +0200
Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-31 09:40 +0200
Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-31 10:00 +0200
Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-08-31 10:10 +0200
Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-31 10:20 +0200
Re: WARNING: possible circular locking dependency detected Thomas Gleixner <tglx@linutronix.de> - 2017-08-31 23:30 +0200
Re: WARNING: possible circular locking dependency detected Peter Zijlstra <peterz@infradead.org> - 2017-09-01 22:40 +0200
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