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From: Dmitry Vyukov <dvyukov@google.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jan Kara <jack@suse.cz>,
	syzbot 
	<bot+f99f3a0db9007f4f4e32db54229a240c4fe57c15@syzkaller.appspotmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	jlayton@redhat.com, LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, npiggin@gmail.com, rgoldwyn@suse.com,
	ross.zwisler@linux.intel.com, syzkaller-bugs@googlegroups.com,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: possible deadlock in generic_file_write_iter
Date: Mon, 6 Nov 2017 14:35:44 +0100	[thread overview]
Message-ID: <CACT4Y+YHPOaCVO81VPuC9hDLCSx=KJmwRf7pa3b96UAowLmA2A@mail.gmail.com> (raw)
In-Reply-To: <20171106133304.GS21978@ZenIV.linux.org.uk>

On Mon, Nov 6, 2017 at 2:33 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Mon, Nov 06, 2017 at 02:15:44PM +0100, Jan Kara wrote:
>
>> > Should we annotate these inodes with different lock types? Or use
>> > nesting annotations?
>>
>> Well, you'd need to have a completely separate set of locking classes for
>> each filesystem to avoid false positives like these. And that would
>> increase number of classes lockdep has to handle significantly. So I'm not
>> sure it's really worth it...
>
> Especially when you consider that backing file might be on a filesystem
> that lives on another loop device.  *All* per-{device,fs} locks involved
> would need classes split that way...


This crashes our test machines left and right. We've seen 100000+ of
these crashes. We need to do at least something. Can we disable all
checking of these mutexes if they inherently have positives?

+Ingo, Peter, maybe you have some suggestions of how to fight this
lockdep false positives. Full thread is here:
https://groups.google.com/forum/#!msg/syzkaller-bugs/NJ_4llH84XI/c7M9jNLTAgAJ

WARNING: multiple messages have this Message-ID (diff)
From: Dmitry Vyukov <dvyukov@google.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jan Kara <jack@suse.cz>,
	syzbot
	<bot+f99f3a0db9007f4f4e32db54229a240c4fe57c15@syzkaller.appspotmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	jlayton@redhat.com, LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, npiggin@gmail.com, rgoldwyn@suse.com,
	ross.zwisler@linux.intel.com, syzkaller-bugs@googlegroups.com,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: possible deadlock in generic_file_write_iter
Date: Mon, 6 Nov 2017 14:35:44 +0100	[thread overview]
Message-ID: <CACT4Y+YHPOaCVO81VPuC9hDLCSx=KJmwRf7pa3b96UAowLmA2A@mail.gmail.com> (raw)
In-Reply-To: <20171106133304.GS21978@ZenIV.linux.org.uk>

On Mon, Nov 6, 2017 at 2:33 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Mon, Nov 06, 2017 at 02:15:44PM +0100, Jan Kara wrote:
>
>> > Should we annotate these inodes with different lock types? Or use
>> > nesting annotations?
>>
>> Well, you'd need to have a completely separate set of locking classes for
>> each filesystem to avoid false positives like these. And that would
>> increase number of classes lockdep has to handle significantly. So I'm not
>> sure it's really worth it...
>
> Especially when you consider that backing file might be on a filesystem
> that lives on another loop device.  *All* per-{device,fs} locks involved
> would need classes split that way...


This crashes our test machines left and right. We've seen 100000+ of
these crashes. We need to do at least something. Can we disable all
checking of these mutexes if they inherently have positives?

+Ingo, Peter, maybe you have some suggestions of how to fight this
lockdep false positives. Full thread is here:
https://groups.google.com/forum/#!msg/syzkaller-bugs/NJ_4llH84XI/c7M9jNLTAgAJ

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  reply	other threads:[~2017-11-06 13:36 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-05 10:25 possible deadlock in generic_file_write_iter syzbot
2017-11-05 10:25 ` syzbot
2017-11-05 10:39 ` Dmitry Vyukov
2017-11-05 10:39   ` Dmitry Vyukov
2017-11-05 10:39   ` Dmitry Vyukov
2017-11-06  3:29 ` Al Viro
2017-11-06  3:29   ` Al Viro
2017-11-06  6:32   ` Dmitry Vyukov
2017-11-06  6:32     ` Dmitry Vyukov
2017-11-06 13:15     ` Jan Kara
2017-11-06 13:15       ` Jan Kara
2017-11-06 13:33       ` Al Viro
2017-11-06 13:33         ` Al Viro
2017-11-06 13:35         ` Dmitry Vyukov [this message]
2017-11-06 13:35           ` Dmitry Vyukov
2017-11-06 16:01           ` Peter Zijlstra
2017-11-06 16:01             ` Peter Zijlstra
2017-11-06 17:36             ` Christoph Hellwig
2017-11-06 17:36               ` Christoph Hellwig
2017-11-06 23:45               ` Matthew Wilcox
2017-11-06 23:45                 ` Matthew Wilcox
2017-11-07  0:54             ` Byungchul Park
2017-11-07  0:54               ` Byungchul Park
2017-11-07  8:11               ` Peter Zijlstra
2017-11-07  8:11                 ` Peter Zijlstra
2017-11-07  8:18                 ` Dmitry Vyukov
2017-11-07  8:18                   ` Dmitry Vyukov
2017-11-07  8:30                 ` Byungchul Park
2017-11-07  8:30                   ` Byungchul Park
2017-11-07  8:31                   ` Dmitry Vyukov
2017-11-07  8:31                     ` Dmitry Vyukov
2017-11-07  8:42                     ` Byungchul Park
2017-11-07  8:42                       ` Byungchul Park

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