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Date: Tue, 24 Aug 2021 16:12:33 -0700
From: Song Liu <song@...nel.org>
To: syzbot <syzbot+fadc0aaf497e6a493b9f@...kaller.appspotmail.com>,
Christoph Hellwig <hch@....de>,
Christoph Hellwig <hch@...radead.org>
Cc: open list <linux-kernel@...r.kernel.org>,
linux-raid <linux-raid@...r.kernel.org>,
syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] possible deadlock in md_open
Hi Christoph,
On Tue, Aug 24, 2021 at 11:19 AM syzbot
<syzbot+fadc0aaf497e6a493b9f@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 372b2891c15a Add linux-next specific files for 20210824
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=124dca75300000
> kernel config: https://syzkaller.appspot.com/x/.config?x=18ce42745c8b0dd6
> dashboard link: https://syzkaller.appspot.com/bug?extid=fadc0aaf497e6a493b9f
> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13b10d05300000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13fa60fe300000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+fadc0aaf497e6a493b9f@...kaller.appspotmail.com
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.14.0-rc7-next-20210824-syzkaller #0 Not tainted
> ------------------------------------------------------
> syz-executor325/6558 is trying to acquire lock:
> ffff888013f90230 (&mddev->open_mutex){+.+.}-{3:3}, at: md_open+0xfd/0x2e0 drivers/md/md.c:7815
>
> but task is already holding lock:
> ffff888077ce3118 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_get_by_dev.part.0+0x9b/0xb60 fs/block_dev.c:1227
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&disk->open_mutex){+.+.}-{3:3}:
> __mutex_lock_common kernel/locking/mutex.c:596 [inline]
> __mutex_lock+0x131/0x12f0 kernel/locking/mutex.c:729
> bd_register_pending_holders+0x2c/0x470 block/holder.c:160
I looked into this and found the error was triggered by
d62633873590 ("block: support delayed holder registration")
But I am not quite sure how to fix it. Do you have some suggestions on
this?
Thanks,
Song
> device_add_disk+0x75e/0xfd0 block/genhd.c:505
> add_disk include/linux/genhd.h:221 [inline]
> md_alloc+0x91d/0x1150 drivers/md/md.c:5707
> md_probe+0x69/0x70 drivers/md/md.c:5738
> blk_request_module+0x111/0x1d0 block/genhd.c:667
> blkdev_get_no_open+0x178/0x1e0 fs/block_dev.c:1150
> blkdev_get_by_dev.part.0+0x22/0xb60 fs/block_dev.c:1214
> blkdev_get_by_dev+0x6b/0x80 fs/block_dev.c:1267
> swsusp_check+0x4d/0x270 kernel/power/swap.c:1525
> software_resume.part.0+0x102/0x1f0 kernel/power/hibernate.c:977
> software_resume kernel/power/hibernate.c:86 [inline]
> resume_store+0x161/0x190 kernel/power/hibernate.c:1179
> kobj_attr_store+0x50/0x80 lib/kobject.c:856
> sysfs_kf_write+0x110/0x160 fs/sysfs/file.c:139
> kernfs_fop_write_iter+0x342/0x500 fs/kernfs/file.c:296
> call_write_iter include/linux/fs.h:2163 [inline]
> new_sync_write+0x429/0x660 fs/read_write.c:511
> vfs_write+0x7cf/0xae0 fs/read_write.c:598
> ksys_write+0x12d/0x250 fs/read_write.c:651
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> -> #0 (&mddev->open_mutex){+.+.}-{3:3}:
> check_prev_add kernel/locking/lockdep.c:3051 [inline]
> check_prevs_add kernel/locking/lockdep.c:3174 [inline]
> validate_chain kernel/locking/lockdep.c:3789 [inline]
> __lock_acquire+0x2a07/0x54a0 kernel/locking/lockdep.c:5015
> lock_acquire kernel/locking/lockdep.c:5625 [inline]
> lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
> __mutex_lock_common kernel/locking/mutex.c:596 [inline]
> __mutex_lock+0x131/0x12f0 kernel/locking/mutex.c:729
> md_open+0xfd/0x2e0 drivers/md/md.c:7815
> blkdev_get_whole+0x99/0x2a0 fs/block_dev.c:1079
> blkdev_get_by_dev.part.0+0x354/0xb60 fs/block_dev.c:1234
> blkdev_get_by_dev+0x6b/0x80 fs/block_dev.c:1267
> swsusp_check+0x4d/0x270 kernel/power/swap.c:1525
> software_resume.part.0+0x102/0x1f0 kernel/power/hibernate.c:977
> software_resume kernel/power/hibernate.c:86 [inline]
> resume_store+0x161/0x190 kernel/power/hibernate.c:1179
> kobj_attr_store+0x50/0x80 lib/kobject.c:856
> sysfs_kf_write+0x110/0x160 fs/sysfs/file.c:139
> kernfs_fop_write_iter+0x342/0x500 fs/kernfs/file.c:296
> call_write_iter include/linux/fs.h:2163 [inline]
> new_sync_write+0x429/0x660 fs/read_write.c:511
> vfs_write+0x7cf/0xae0 fs/read_write.c:598
> ksys_write+0x12d/0x250 fs/read_write.c:651
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&disk->open_mutex);
> lock(&mddev->open_mutex);
> lock(&disk->open_mutex);
> lock(&mddev->open_mutex);
>
> *** DEADLOCK ***
>
> 5 locks held by syz-executor325/6558:
> #0: ffff88807f6bc460 (sb_writers#6){.+.+}-{0:0}, at: ksys_write+0x12d/0x250 fs/read_write.c:651
> #1: ffff88801a6a3488 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x287/0x500 fs/kernfs/file.c:287
> #2: ffff8881441a6830 (kn->active#90){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x2ab/0x500 fs/kernfs/file.c:288
> #3: ffffffff8b84fc68 (system_transition_mutex/1){+.+.}-{3:3}, at: software_resume.part.0+0x19/0x1f0 kernel/power/hibernate.c:932
> #4: ffff888077ce3118 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_get_by_dev.part.0+0x9b/0xb60 fs/block_dev.c:1227
>
> stack backtrace:
> CPU: 1 PID: 6558 Comm: syz-executor325 Not tainted 5.14.0-rc7-next-20210824-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
> check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2131
> check_prev_add kernel/locking/lockdep.c:3051 [inline]
> check_prevs_add kernel/locking/lockdep.c:3174 [inline]
> validate_chain kernel/locking/lockdep.c:3789 [inline]
> __lock_acquire+0x2a07/0x54a0 kernel/locking/lockdep.c:5015
> lock_acquire kernel/locking/lockdep.c:5625 [inline]
> lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
> __mutex_lock_common kernel/locking/mutex.c:596 [inline]
> __mutex_lock+0x131/0x12f0 kernel/locking/mutex.c:729
> md_open+0xfd/0x2e0 drivers/md/md.c:7815
> blkdev_get_whole+0x99/0x2a0 fs/block_dev.c:1079
> blkdev_get_by_dev.part.0+0x354/0xb60 fs/block_dev.c:1234
> blkdev_get_by_dev+0x6b/0x80 fs/block_dev.c:1267
> swsusp_check+0x4d/0x270 kernel/power/swap.c:1525
> software_resume.part.0+0x102/0x1f0 kernel/power/hibernate.c:977
> software_resume kernel/power/hibernate.c:86 [inline]
> resume_store+0x161/0x190 kernel/power/hibernate.c:1179
> kobj_attr_store+0x50/0x80 lib/kobject.c:856
> sysfs_kf_write+0x110/0x160 fs/sysfs/file.c:139
> kernfs_fop_write_iter+0x342/0x500 fs/kernfs/file.c:296
> call_write_iter include/linux/fs.h:2163 [inline]
> new_sync_write+0x429/0x660 fs/read_write.c:511
> vfs_write+0x7cf/0xae0 fs/read_write.c:598
> ksys_write+0x12d/0x250 fs/read_write.c:651
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x43f0e9
> Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffd59408358 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 0000000000400488 RCX: 000000000043f0e9
> RDX: 000000000000fdef RSI: 0000000020000000 RDI: 0000000000000003
> RBP: 0000000000402e40 R08: 0000000000000012 R09: 0000000000400488
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402ed0
> R13: 0000000000000000 R14: 00000000004ad018 R15: 0000000000400488
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
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