Re: possible deadlock in blkdev_put

[Jan Kara]

Looks like btrfs issue. Adding relevant people to CC.

On Mon 21-09-20 02:32:21, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    325d0eab Merge branch 'akpm' (patches from Andrew)
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=102425d9900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=b12e84189082991c
> dashboard link: https://syzkaller.appspot.com/bug?extid=84a0634dc5d21d488419
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+84a0634dc5d21d488419@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.9.0-rc5-syzkaller #0 Not tainted
> ------------------------------------------------------
> syz-executor.0/6878 is trying to acquire lock:
> ffff88804c17d780 (&bdev->bd_mutex){+.+.}-{3:3}, at: blkdev_put+0x30/0x520 fs/block_dev.c:1804
> 
> but task is already holding lock:
> ffff8880908cfce0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: close_fs_devices.part.0+0x2e/0x800 fs/btrfs/volumes.c:1159
> 
> which lock already depends on the new lock.
> 
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #4 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
>        __mutex_lock_common kernel/locking/mutex.c:956 [inline]
>        __mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
>        btrfs_finish_chunk_alloc+0x281/0xf90 fs/btrfs/volumes.c:5255
>        btrfs_create_pending_block_groups+0x2f3/0x700 fs/btrfs/block-group.c:2109
>        __btrfs_end_transaction+0xf5/0x690 fs/btrfs/transaction.c:916
>        find_free_extent_update_loop fs/btrfs/extent-tree.c:3807 [inline]
>        find_free_extent+0x23b7/0x2e60 fs/btrfs/extent-tree.c:4127
>        btrfs_reserve_extent+0x166/0x460 fs/btrfs/extent-tree.c:4206
>        cow_file_range+0x3de/0x9b0 fs/btrfs/inode.c:1063
>        btrfs_run_delalloc_range+0x2cf/0x1410 fs/btrfs/inode.c:1838
>        writepage_delalloc+0x150/0x460 fs/btrfs/extent_io.c:3439
>        __extent_writepage+0x441/0xd00 fs/btrfs/extent_io.c:3653
>        extent_write_cache_pages.constprop.0+0x69d/0x1040 fs/btrfs/extent_io.c:4249
>        extent_writepages+0xcd/0x2b0 fs/btrfs/extent_io.c:4370
>        do_writepages+0xec/0x290 mm/page-writeback.c:2352
>        __writeback_single_inode+0x125/0x1400 fs/fs-writeback.c:1461
>        writeback_sb_inodes+0x53d/0xf40 fs/fs-writeback.c:1721
>        wb_writeback+0x2ad/0xd40 fs/fs-writeback.c:1894
>        wb_do_writeback fs/fs-writeback.c:2039 [inline]
>        wb_workfn+0x2dc/0x13e0 fs/fs-writeback.c:2080
>        process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
>        worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
>        kthread+0x3b5/0x4a0 kernel/kthread.c:292
>        ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> 
> -> #3 (sb_internal#2){.+.+}-{0:0}:
>        percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
>        __sb_start_write+0x234/0x470 fs/super.c:1672
>        sb_start_intwrite include/linux/fs.h:1690 [inline]
>        start_transaction+0xbe7/0x1170 fs/btrfs/transaction.c:624
>        find_free_extent_update_loop fs/btrfs/extent-tree.c:3789 [inline]
>        find_free_extent+0x25e1/0x2e60 fs/btrfs/extent-tree.c:4127
>        btrfs_reserve_extent+0x166/0x460 fs/btrfs/extent-tree.c:4206
>        cow_file_range+0x3de/0x9b0 fs/btrfs/inode.c:1063
>        btrfs_run_delalloc_range+0x2cf/0x1410 fs/btrfs/inode.c:1838
>        writepage_delalloc+0x150/0x460 fs/btrfs/extent_io.c:3439
>        __extent_writepage+0x441/0xd00 fs/btrfs/extent_io.c:3653
>        extent_write_cache_pages.constprop.0+0x69d/0x1040 fs/btrfs/extent_io.c:4249
>        extent_writepages+0xcd/0x2b0 fs/btrfs/extent_io.c:4370
>        do_writepages+0xec/0x290 mm/page-writeback.c:2352
>        __writeback_single_inode+0x125/0x1400 fs/fs-writeback.c:1461
>        writeback_sb_inodes+0x53d/0xf40 fs/fs-writeback.c:1721
>        wb_writeback+0x2ad/0xd40 fs/fs-writeback.c:1894
>        wb_do_writeback fs/fs-writeback.c:2039 [inline]
>        wb_workfn+0x2dc/0x13e0 fs/fs-writeback.c:2080
>        process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
>        worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
>        kthread+0x3b5/0x4a0 kernel/kthread.c:292
>        ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> 
> -> #2 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}:
>        __flush_work+0x60e/0xac0 kernel/workqueue.c:3041
>        wb_shutdown+0x180/0x220 mm/backing-dev.c:355
>        bdi_unregister+0x174/0x590 mm/backing-dev.c:872
>        del_gendisk+0x820/0xa10 block/genhd.c:933
>        loop_remove drivers/block/loop.c:2192 [inline]
>        loop_control_ioctl drivers/block/loop.c:2291 [inline]
>        loop_control_ioctl+0x3b1/0x480 drivers/block/loop.c:2257
>        vfs_ioctl fs/ioctl.c:48 [inline]
>        __do_sys_ioctl fs/ioctl.c:753 [inline]
>        __se_sys_ioctl fs/ioctl.c:739 [inline]
>        __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
>        do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>        entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> -> #1 (loop_ctl_mutex){+.+.}-{3:3}:
>        __mutex_lock_common kernel/locking/mutex.c:956 [inline]
>        __mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
>        lo_open+0x19/0xd0 drivers/block/loop.c:1893
>        __blkdev_get+0x759/0x1aa0 fs/block_dev.c:1507
>        blkdev_get fs/block_dev.c:1639 [inline]
>        blkdev_open+0x227/0x300 fs/block_dev.c:1753
>        do_dentry_open+0x4b9/0x11b0 fs/open.c:817
>        do_open fs/namei.c:3251 [inline]
>        path_openat+0x1b9a/0x2730 fs/namei.c:3368
>        do_filp_open+0x17e/0x3c0 fs/namei.c:3395
>        do_sys_openat2+0x16d/0x420 fs/open.c:1168
>        do_sys_open fs/open.c:1184 [inline]
>        __do_sys_open fs/open.c:1192 [inline]
>        __se_sys_open fs/open.c:1188 [inline]
>        __x64_sys_open+0x119/0x1c0 fs/open.c:1188
>        do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>        entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> -> #0 (&bdev->bd_mutex){+.+.}-{3:3}:
>        check_prev_add kernel/locking/lockdep.c:2496 [inline]
>        check_prevs_add kernel/locking/lockdep.c:2601 [inline]
>        validate_chain kernel/locking/lockdep.c:3218 [inline]
>        __lock_acquire+0x2a96/0x5780 kernel/locking/lockdep.c:4426
>        lock_acquire+0x1f3/0xae0 kernel/locking/lockdep.c:5006
>        __mutex_lock_common kernel/locking/mutex.c:956 [inline]
>        __mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
>        blkdev_put+0x30/0x520 fs/block_dev.c:1804
>        btrfs_close_bdev fs/btrfs/volumes.c:1117 [inline]
>        btrfs_close_bdev fs/btrfs/volumes.c:1107 [inline]
>        btrfs_close_one_device fs/btrfs/volumes.c:1133 [inline]
>        close_fs_devices.part.0+0x1a4/0x800 fs/btrfs/volumes.c:1161
>        close_fs_devices fs/btrfs/volumes.c:1193 [inline]
>        btrfs_close_devices+0x95/0x1f0 fs/btrfs/volumes.c:1179
>        close_ctree+0x688/0x6cb fs/btrfs/disk-io.c:4149
>        generic_shutdown_super+0x144/0x370 fs/super.c:464
>        kill_anon_super+0x36/0x60 fs/super.c:1108
>        btrfs_kill_super+0x38/0x50 fs/btrfs/super.c:2265
>        deactivate_locked_super+0x94/0x160 fs/super.c:335
>        deactivate_super+0xad/0xd0 fs/super.c:366
>        cleanup_mnt+0x3a3/0x530 fs/namespace.c:1118
>        task_work_run+0xdd/0x190 kernel/task_work.c:141
>        tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>        exit_to_user_mode_loop kernel/entry/common.c:163 [inline]
>        exit_to_user_mode_prepare+0x1e1/0x200 kernel/entry/common.c:190
>        syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:265
>        entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> other info that might help us debug this:
> 
> Chain exists of:
>   &bdev->bd_mutex --> sb_internal#2 --> &fs_devs->device_list_mutex
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(&fs_devs->device_list_mutex);
>                                lock(sb_internal#2);
>                                lock(&fs_devs->device_list_mutex);
>   lock(&bdev->bd_mutex);
> 
>  *** DEADLOCK ***
> 
> 3 locks held by syz-executor.0/6878:
>  #0: ffff88809070c0e0 (&type->s_umount_key#70){++++}-{3:3}, at: deactivate_super+0xa5/0xd0 fs/super.c:365
>  #1: ffffffff8a5b37a8 (uuid_mutex){+.+.}-{3:3}, at: btrfs_close_devices+0x23/0x1f0 fs/btrfs/volumes.c:1178
>  #2: ffff8880908cfce0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: close_fs_devices.part.0+0x2e/0x800 fs/btrfs/volumes.c:1159
> 
> stack backtrace:
> CPU: 0 PID: 6878 Comm: syz-executor.0 Not tainted 5.9.0-rc5-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x198/0x1fd lib/dump_stack.c:118
>  check_noncircular+0x324/0x3e0 kernel/locking/lockdep.c:1827
>  check_prev_add kernel/locking/lockdep.c:2496 [inline]
>  check_prevs_add kernel/locking/lockdep.c:2601 [inline]
>  validate_chain kernel/locking/lockdep.c:3218 [inline]
>  __lock_acquire+0x2a96/0x5780 kernel/locking/lockdep.c:4426
>  lock_acquire+0x1f3/0xae0 kernel/locking/lockdep.c:5006
>  __mutex_lock_common kernel/locking/mutex.c:956 [inline]
>  __mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
>  blkdev_put+0x30/0x520 fs/block_dev.c:1804
>  btrfs_close_bdev fs/btrfs/volumes.c:1117 [inline]
>  btrfs_close_bdev fs/btrfs/volumes.c:1107 [inline]
>  btrfs_close_one_device fs/btrfs/volumes.c:1133 [inline]
>  close_fs_devices.part.0+0x1a4/0x800 fs/btrfs/volumes.c:1161
>  close_fs_devices fs/btrfs/volumes.c:1193 [inline]
>  btrfs_close_devices+0x95/0x1f0 fs/btrfs/volumes.c:1179
>  close_ctree+0x688/0x6cb fs/btrfs/disk-io.c:4149
>  generic_shutdown_super+0x144/0x370 fs/super.c:464
>  kill_anon_super+0x36/0x60 fs/super.c:1108
>  btrfs_kill_super+0x38/0x50 fs/btrfs/super.c:2265
>  deactivate_locked_super+0x94/0x160 fs/super.c:335
>  deactivate_super+0xad/0xd0 fs/super.c:366
>  cleanup_mnt+0x3a3/0x530 fs/namespace.c:1118
>  task_work_run+0xdd/0x190 kernel/task_work.c:141
>  tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:163 [inline]
>  exit_to_user_mode_prepare+0x1e1/0x200 kernel/entry/common.c:190
>  syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:265
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x460027
> Code: 64 89 04 25 d0 02 00 00 58 5f ff d0 48 89 c7 e8 2f be ff ff 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 a6 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 fd 89 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fff59216328 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
> RAX: 0000000000000000 RBX: 0000000000076035 RCX: 0000000000460027
> RDX: 0000000000403188 RSI: 0000000000000002 RDI: 00007fff592163d0
> RBP: 0000000000000333 R08: 0000000000000000 R09: 000000000000000b
> R10: 0000000000000005 R11: 0000000000000246 R12: 00007fff59217460
> R13: 0000000002df2a60 R14: 0000000000000000 R15: 00007fff59217460
> 
> 
> ---
> 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@xxxxxxxxxxxxxxxx.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR