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From: Tyler Hicks <tyhicks@linux.microsoft.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Stefan Haberland <sth@linux.ibm.com>,
	Jan Hoeppner <hoeppner@linux.ibm.com>,
	linux-block <linux-block@vger.kernel.org>,
	syzbot <syzbot+61e04e51b7ac86930589@syzkaller.appspotmail.com>,
	Petr Vorel <pvorel@suse.cz>,
	Pavel Tatashin <pasha.tatashin@soleen.com>,
	Tejun Heo <tj@kernel.org>
Subject: Re: [syzbot] possible deadlock in del_gendisk
Date: Wed, 9 Jun 2021 11:46:39 -0500	[thread overview]
Message-ID: <20210609164639.GM4910@sequoia> (raw)
In-Reply-To: <7b8c9eeb-789d-e5e6-04d6-130ee8be7305@i-love.sakura.ne.jp>

On 2021-06-10 01:31:17, Tetsuo Handa wrote:
> Hello, Christoph.
> 
> I'm currently trying full bisection.
> 
>   # bad: [fc0586062816559defb14c947319ef8c4c326fb3] Merge tag 'for-5.13/drivers-2021-04-27' of git://git.kernel.dk/linux-block
>   # good: [42dec9a936e7696bea1f27d3c5a0068cd9aa95fd] Merge tag 'perf-core-2021-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
>   # good: [68a32ba14177d4a21c4a9a941cf1d7aea86d436f] Merge tag 'drm-next-2021-04-28' of git://anongit.freedesktop.org/drm/drm
>   # good: [a800abd3ecb9acc55821f7ac9bba6c956b36a595] net: enetc: move skb creation into enetc_build_skb
>   # good: [6cc8e7430801fa238bd7d3acae1eb406c6e02fe1] loop: scale loop device by introducing per device lock

Thanks for doing this. I haven't had a chance to retry this commit with
lockdep but I did re-review it and didn't think that it would be the
cause of this lockdep report since it strictly reduced the usage of the
loop_ctl_mutex.

Tyler

>   git bisect start 'fc0586062816559defb14c947319ef8c4c326fb3' '42dec9a936e7696bea1f27d3c5a0068cd9aa95fd' '68a32ba14177d4a21c4a9a941cf1d7aea86d436f' 'a800abd3ecb9acc55821f7ac9bba6c956b36a595' '6cc8e7430801fa238bd7d3acae1eb406c6e02fe1'
>   # good: [2958a995edc94654df690318df7b9b49e5a3ef88] block/rnbd-clt: Support polling mode for IO latency optimization
>   git bisect good 2958a995edc94654df690318df7b9b49e5a3ef88
> 
> I think we will bisect this problem to
> 
>   commit c76f48eb5c084b1e ("block: take bd_mutex around delete_partitions in del_gendisk")
> 
> because that commit introduced new locking dependency bdev_lookup_sem => disk->part0->bd_mutex
> which matches the lockdep's report.
> 
>   ======================================================
>   WARNING: possible circular locking dependency detected
>   5.12.0-rc6-next-20210409-syzkaller #0 Not tainted
>   ------------------------------------------------------
>   syz-executor.4/10285 is trying to acquire lock:
>   ffff8881423245a0 (&bdev->bd_mutex){+.+.}-{3:3}, at: del_gendisk+0x250/0x9e0 block/genhd.c:618
>   
>   but task is already holding lock:
>   ffffffff8c7d9430 (bdev_lookup_sem){++++}-{3:3}, at: del_gendisk+0x222/0x9e0 block/genhd.c:616
> 
> Do we need to revert "partition iteration simplifications" work?
> 
> On 2021/06/07 19:56, Tetsuo Handa wrote:
> > Hello.
> > 
> > syzbot is reporting "possible deadlock in del_gendisk" problem.
> > 
> > I guess this is caused by commit 6cc8e7430801fa23 ("loop: scale loop device
> > by introducing per device lock") because it touches loop_ctl_mutex usage
> > between v5.11 and v5.12-rc1. Please have a look.
> > 
> > On 2021/04/14 2:33, syzbot wrote:
> >> Hello,
> >>
> >> syzbot found the following issue on:
> >>
> >> HEAD commit:    e99d8a84 Add linux-next specific files for 20210409
> >> git tree:       linux-next
> >> console output: https://syzkaller.appspot.com/x/log.txt?x=13b01681d00000
> >> kernel config:  https://syzkaller.appspot.com/x/.config?x=7cd69574979bfeb7
> >> dashboard link: https://syzkaller.appspot.com/bug?extid=61e04e51b7ac86930589
> >> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=148265d9d00000
> >> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16a981a1d00000
> > 
> 

  reply	other threads:[~2021-06-09 16:46 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-13 17:33 [syzbot] possible deadlock in del_gendisk syzbot
2021-04-13 17:41 ` Steven Rostedt
2021-04-13 17:43   ` Steven Rostedt
2021-04-13 18:24     ` Dmitry Vyukov
2021-04-13 18:40       ` Steven Rostedt
2021-04-13 18:43         ` Steven Rostedt
2021-04-16  7:51           ` Bisections with different bug manifestations Dmitry Vyukov
2021-04-16 13:13             ` Steven Rostedt
2021-04-16 13:26               ` Dmitry Vyukov
2021-04-16 13:48                 ` Dmitry Vyukov
2021-06-07 10:56 ` [syzbot] possible deadlock in del_gendisk Tetsuo Handa
2021-06-09 16:31   ` Tetsuo Handa
2021-06-09 16:46     ` Tyler Hicks [this message]
2021-06-10 13:37       ` Tetsuo Handa
2021-06-11  6:46         ` Tetsuo Handa
2021-06-11 15:14           ` [PATCH] loop: drop loop_ctl_mutex around del_gendisk() in loop_remove() Tetsuo Handa
2021-06-15  5:30             ` Tetsuo Handa
2021-06-15  5:31               ` syzbot
2021-06-15  9:04             ` Jan Kara
2021-06-11 14:47       ` [syzbot] possible deadlock in del_gendisk Tetsuo Handa
2021-06-11 15:11         ` Pavel Tatashin
2021-06-11 15:18           ` Pavel Tatashin
2021-06-11 15:49             ` Tetsuo Handa
2021-06-12  2:35               ` Tetsuo Handa
2021-06-13 11:01                 ` Tetsuo Handa

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