From: Thomas Gleixner <tglx@linutronix.de>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, Andrey Ryabinin <aryabinin@virtuozzo.com>,
Michal Hocko <mhocko@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [patch V2 2/2] mm/memory-hotplug: Switch locking to a percpu rwsem
Date: Tue, 4 Jul 2017 14:49:47 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.20.1707041449220.9000@nanos> (raw)
In-Reply-To: <cec30e21-c407-9ffa-c10b-0aa2ea64de2a@suse.cz>
On Tue, 4 Jul 2017, Vlastimil Babka wrote:
> On 07/04/2017 11:32 AM, Thomas Gleixner wrote:
> > Andrey reported a potential deadlock with the memory hotplug lock and the
> > cpu hotplug lock.
> >
> > The reason is that memory hotplug takes the memory hotplug lock and then
> > calls stop_machine() which calls get_online_cpus(). That's the reverse lock
> > order to get_online_cpus(); get_online_mems(); in mm/slub_common.c
> >
> > The problem has been there forever. The reason why this was never reported
> > is that the cpu hotplug locking had this homebrewn recursive reader writer
> > semaphore construct which due to the recursion evaded the full lock dep
> > coverage. The memory hotplug code copied that construct verbatim and
> > therefor has similar issues.
> >
> > Three steps to fix this:
> >
> > 1) Convert the memory hotplug locking to a per cpu rwsem so the potential
> > issues get reported proper by lockdep.
> >
> > 2) Lock the online cpus in mem_hotplug_begin() before taking the memory
> > hotplug rwsem and use stop_machine_cpuslocked() in the page_alloc code
> > and use to avoid recursive locking.
>
> ^ s/and use // ?
Ooops, yes.
Thanks,
tglx
next prev parent reply other threads:[~2017-07-04 12:49 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-04 9:32 [patch V2 0/2] mm/memory_hotplug: Cure potential deadlocks vs. cpu hotplug lock Thomas Gleixner
2017-07-04 9:32 ` [patch V2 1/2] mm: swap: Provide lru_add_drain_all_cpuslocked() Thomas Gleixner
2017-07-04 10:58 ` Michal Hocko
2017-07-04 12:48 ` Thomas Gleixner
2017-07-04 12:52 ` Michal Hocko
2017-07-04 12:07 ` Vlastimil Babka
2017-07-04 12:35 ` Thomas Gleixner
2017-07-04 9:32 ` [patch V2 2/2] mm/memory-hotplug: Switch locking to a percpu rwsem Thomas Gleixner
2017-07-04 10:59 ` Michal Hocko
2017-07-04 12:10 ` Vlastimil Babka
2017-07-04 12:49 ` Thomas Gleixner [this message]
2017-07-04 15:01 ` Davidlohr Bueso
2017-07-04 15:22 ` Davidlohr Bueso
2017-07-04 15:32 ` Thomas Gleixner
2017-07-04 15:42 ` Davidlohr Bueso
2017-07-05 21:53 ` [patch V2 0/2] mm/memory_hotplug: Cure potential deadlocks vs. cpu hotplug lock Andrew Morton
2017-07-06 6:34 ` Thomas Gleixner
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