From: Byungchul Park <byungchul.park@lge.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Dmitry Vyukov <dvyukov@google.com>,
syzbot
<bot+e7353c7141ff7cbb718e4c888a14fa92de41ebaa@syzkaller.appspotmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Dan Williams <dan.j.williams@intel.com>,
Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>,
jglisse@redhat.com, LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, shli@fb.com, syzkaller-bugs@googlegroups.com,
Thomas Gleixner <tglx@linutronix.de>,
Vlastimil Babka <vbabka@suse.cz>,
ying.huang@intel.com, kernel-team@lge.com, peterz@infradead.org
Subject: Re: possible deadlock in lru_add_drain_all
Date: Mon, 30 Oct 2017 19:09:21 +0900 [thread overview]
Message-ID: <20171030100921.GA18085@X58A-UD3R> (raw)
In-Reply-To: <20171030082203.4xvq2af25shfci2z@dhcp22.suse.cz>
On Mon, Oct 30, 2017 at 09:22:03AM +0100, Michal Hocko wrote:
> [Cc Byungchul. The original full report is
> http://lkml.kernel.org/r/089e0825eec8955c1f055c83d476@google.com]
>
> Could you have a look please? This smells like a false positive to me.
+cc peterz@infradead.org
Hello,
IMHO, the false positive was caused by the lockdep_map of 'cpuhp_state'
which couldn't distinguish between cpu-up and cpu-down.
And it was solved with the following commit by Peter and Thomas:
5f4b55e10645b7371322c800a5ec745cab487a6c
smp/hotplug: Differentiate the AP-work lockdep class between up and down
Therefore, we can avoid the false positive on later than the commit.
Peter and Thomas, could you confirm it?
Thanks,
Byungchul
> On Fri 27-10-17 15:42:34, Michal Hocko wrote:
> > On Fri 27-10-17 11:44:58, Dmitry Vyukov wrote:
> > > On Fri, Oct 27, 2017 at 11:34 AM, Michal Hocko <mhocko@kernel.org> wrote:
> > > > On Fri 27-10-17 02:22:40, syzbot wrote:
> > > >> Hello,
> > > >>
> > > >> syzkaller hit the following crash on
> > > >> a31cc455c512f3f1dd5f79cac8e29a7c8a617af8
> > > >> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> > > >> compiler: gcc (GCC) 7.1.1 20170620
> > > >> .config is attached
> > > >> Raw console output is attached.
> > > >
> > > > I do not see such a commit. My linux-next top is next-20171018
> > > >
> > > > [...]
> > > >> Chain exists of:
> > > >> cpu_hotplug_lock.rw_sem --> &pipe->mutex/1 --> &sb->s_type->i_mutex_key#9
> > > >>
> > > >> Possible unsafe locking scenario:
> > > >>
> > > >> CPU0 CPU1
> > > >> ---- ----
> > > >> lock(&sb->s_type->i_mutex_key#9);
> > > >> lock(&pipe->mutex/1);
> > > >> lock(&sb->s_type->i_mutex_key#9);
> > > >> lock(cpu_hotplug_lock.rw_sem);
> > > >
> > > > I am quite confused about this report. Where exactly is the deadlock?
> > > > I do not see where we would get pipe mutex from inside of the hotplug
> > > > lock. Is it possible this is just a false possitive due to cross release
> > > > feature?
> > >
> > >
> > > As far as I understand this CPU0/CPU1 scheme works only for simple
> > > cases with 2 mutexes. This seem to have larger cycle as denoted by
> > > "the existing dependency chain (in reverse order) is:" section.
> >
> > My point was that lru_add_drain_all doesn't take any external locks
> > other than lru_lock and that one is not anywhere in the chain AFAICS.
> >
> > --
> > Michal Hocko
> > SUSE Labs
>
> --
> Michal Hocko
> SUSE Labs
next prev parent reply other threads:[~2017-10-30 10:09 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <089e0825eec8955c1f055c83d476@google.com>
2017-10-27 9:34 ` possible deadlock in lru_add_drain_all Michal Hocko
2017-10-27 9:44 ` Dmitry Vyukov
2017-10-27 9:47 ` Dmitry Vyukov
2017-10-27 13:42 ` Michal Hocko
2017-10-30 8:22 ` Michal Hocko
2017-10-30 10:09 ` Byungchul Park [this message]
2017-10-30 15:10 ` Peter Zijlstra
2017-10-30 15:22 ` Peter Zijlstra
2017-10-31 13:13 ` Michal Hocko
2017-10-31 13:51 ` Peter Zijlstra
2017-10-31 13:55 ` Dmitry Vyukov
2017-10-31 14:52 ` Peter Zijlstra
2017-10-31 14:58 ` Michal Hocko
2017-10-31 15:10 ` Peter Zijlstra
2017-11-01 8:59 ` Byungchul Park
2017-11-01 12:01 ` Peter Zijlstra
2017-11-01 23:54 ` Byungchul Park
2018-02-14 14:01 ` Dmitry Vyukov
2018-02-14 15:44 ` Michal Hocko
2018-02-14 15:57 ` Dmitry Vyukov
2017-10-31 15:25 ` Peter Zijlstra
2017-10-31 15:45 ` Michal Hocko
2017-10-31 16:30 ` Peter Zijlstra
2017-11-01 8:31 ` Byungchul Park
2017-10-30 10:26 ` Byungchul Park
2017-10-30 11:48 ` Michal Hocko
2017-10-27 11:27 ` Vlastimil Babka
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