possible deadlock in blkdev_put

Status: auto-closed as invalid on 2021/01/18 22:03
Subsystems: btrfs
[Documentation on labels]
Reported-by: syzbot+84a0634dc5d21d488419@syzkaller.appspotmail.com
First crash: 2146d, last: 2146d
▶ ▼ Discussions (3)
Title Replies (including bot) Last reply
[PATCH 5.8 000/124] 5.8.15-rc1 review 136 (136) 2020/10/14 18:31
[PATCH AUTOSEL 5.8 01/12] epoll: do not insert into poll queues until all sanity checks are done 13 (13) 2020/10/05 16:03
possible deadlock in blkdev_put 2 (3) 2020/09/22 11:01
▶ ▼ Similar bugs (8)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in blkdev_put (4) block 4 2 1011d 1025d 0/29 auto-obsoleted due to no activity on 2024/02/07 19:21
linux-4.19 possible deadlock in blkdev_put btrfs 4 syz, C error 2 1284d 1313d 0/1 upstream: reported C repro on 2023/01/01 16:48
upstream possible deadlock in blkdev_put (3) block exfat 4 syz, C 870 1536d 1608d 22/29 fixed on 2023/02/24 13:50
upstream possible deadlock in blkdev_put (2) exfat block 4 syz, C done 502 1612d 1714d 20/29 fixed on 2022/03/08 16:11
linux-6.1 possible deadlock in blkdev_put 4 1 26d 26d 0/3 upstream: reported on 2026/07/12 08:46
linux-6.6 possible deadlock in blkdev_put (2) 4 5 87d 115d 0/2 upstream: reported on 2026/04/13 15:25
linux-6.6 possible deadlock in blkdev_put 4 4 220d 323d 0/2 auto-obsoleted due to no activity on 2026/04/08 12:30
linux-4.14 possible deadlock in blkdev_put 4 syz, C 5 1264d 2136d 0/1 upstream: reported C repro on 2020/10/01 09:27

Sample crash report:
======================================================
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

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2020/09/20 22:02 upstream 325d0eab4f31 9564d2e9 .config console log report info ci-upstream-kasan-gce-selinux-root
* Struck through repros no longer work on HEAD.