syzbot

BTRFS info (device loop0): clearing free space tree
BTRFS info (device loop0): clearing compat-ro feature flag for FREE_SPACE_TREE (0x1)
BTRFS info (device loop0): clearing compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/4354 is trying to acquire lock:
ffff88805bde8610 (&type->i_mutex_dir_key#8){++++}-{3:3}, at: inode_lock_shared include/linux/fs.h:797 [inline]
ffff88805bde8610 (&type->i_mutex_dir_key#8){++++}-{3:3}, at: lookup_slow+0x46/0x70 fs/namei.c:1687

but task is already holding lock:
ffff88805cef50e0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: btrfs_free_stale_devices+0x186/0xa60 fs/btrfs/volumes.c:603

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       btrfs_run_dev_stats+0xdf/0xdf0 fs/btrfs/volumes.c:7991
       commit_cowonly_roots+0x17e/0x9c0 fs/btrfs/transaction.c:1292
       btrfs_commit_transaction+0x1229/0x3440 fs/btrfs/transaction.c:2394
       btrfs_clear_free_space_tree+0x786/0xbf0 fs/btrfs/free-space-tree.c:1264
       btrfs_start_pre_rw_mount+0x287/0x630 fs/btrfs/disk-io.c:3079
       open_ctree+0x2878/0x3250 fs/btrfs/disk-io.c:3634
       btrfs_fill_super+0x1c2/0x2e0 fs/btrfs/super.c:1387
       btrfs_mount_root+0x857/0x8c0 fs/btrfs/super.c:1751
       legacy_get_tree+0xe6/0x180 fs/fs_context.c:611
       vfs_get_tree+0x88/0x270 fs/super.c:1530
       fc_mount fs/namespace.c:1005 [inline]
       vfs_kern_mount+0xba/0x150 fs/namespace.c:1035
       btrfs_mount+0x2d7/0xa50 fs/btrfs/super.c:1811
       legacy_get_tree+0xe6/0x180 fs/fs_context.c:611
       vfs_get_tree+0x88/0x270 fs/super.c:1530
       do_new_mount+0x24a/0xa40 fs/namespace.c:3034
       do_mount fs/namespace.c:3377 [inline]
       __do_sys_mount fs/namespace.c:3585 [inline]
       __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:3562
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #2 (&fs_info->tree_log_mutex){+.+.}-{3:3}:
       __lock_release kernel/locking/lockdep.c:5339 [inline]
       lock_release+0x31a/0x870 kernel/locking/lockdep.c:5643
       __mutex_unlock_slowpath+0xb3/0x6a0 kernel/locking/mutex.c:851
       btrfs_commit_transaction+0x1c11/0x3440 fs/btrfs/transaction.c:2441
       btrfs_clear_free_space_tree+0x786/0xbf0 fs/btrfs/free-space-tree.c:1264
       btrfs_start_pre_rw_mount+0x287/0x630 fs/btrfs/disk-io.c:3079
       open_ctree+0x2878/0x3250 fs/btrfs/disk-io.c:3634
       btrfs_fill_super+0x1c2/0x2e0 fs/btrfs/super.c:1387
       btrfs_mount_root+0x857/0x8c0 fs/btrfs/super.c:1751
       legacy_get_tree+0xe6/0x180 fs/fs_context.c:611
       vfs_get_tree+0x88/0x270 fs/super.c:1530
       fc_mount fs/namespace.c:1005 [inline]
       vfs_kern_mount+0xba/0x150 fs/namespace.c:1035
       btrfs_mount+0x2d7/0xa50 fs/btrfs/super.c:1811
       legacy_get_tree+0xe6/0x180 fs/fs_context.c:611
       vfs_get_tree+0x88/0x270 fs/super.c:1530
       do_new_mount+0x24a/0xa40 fs/namespace.c:3034
       do_mount fs/namespace.c:3377 [inline]
       __do_sys_mount fs/namespace.c:3585 [inline]
       __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:3562
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #1 (sb_internal#2){.+.+}-{0:0}:
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1811 [inline]
       sb_start_intwrite include/linux/fs.h:1928 [inline]
       start_transaction+0x5bc/0x1130 fs/btrfs/transaction.c:680
       btrfs_create+0x103/0x5b0 fs/btrfs/inode.c:6915
       lookup_open fs/namei.c:3470 [inline]
       open_last_lookups fs/namei.c:3540 [inline]
       path_openat+0x11e1/0x2f30 fs/namei.c:3747
       do_filp_open+0x1b3/0x3e0 fs/namei.c:3777
       do_sys_openat2+0x142/0x4a0 fs/open.c:1253
       do_sys_open fs/open.c:1269 [inline]
       __do_sys_openat fs/open.c:1285 [inline]
       __se_sys_openat fs/open.c:1280 [inline]
       __x64_sys_openat+0x135/0x160 fs/open.c:1280
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #0 (&type->i_mutex_dir_key#8){++++}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain kernel/locking/lockdep.c:3788 [inline]
       __lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
       lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
       down_read+0x44/0x2e0 kernel/locking/rwsem.c:1498
       inode_lock_shared include/linux/fs.h:797 [inline]
       lookup_slow+0x46/0x70 fs/namei.c:1687
       walk_component+0x319/0x460 fs/namei.c:1984
       lookup_last fs/namei.c:2439 [inline]
       path_lookupat+0x169/0x440 fs/namei.c:2463
       filename_lookup+0x1e2/0x4f0 fs/namei.c:2492
       kern_path+0x37/0x190 fs/namei.c:2590
       lookup_bdev+0xbd/0x270 block/bdev.c:982
       device_matched fs/btrfs/volumes.c:568 [inline]
       btrfs_free_stale_devices+0x6db/0xa60 fs/btrfs/volumes.c:608
       btrfs_forget_devices+0x52/0x80 fs/btrfs/volumes.c:1431
       btrfs_control_ioctl+0x104/0x220 fs/btrfs/super.c:2450
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:874 [inline]
       __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

Chain exists of:
  &type->i_mutex_dir_key#8 --> &fs_info->tree_log_mutex --> &fs_devs->device_list_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&fs_devs->device_list_mutex);
                               lock(&fs_info->tree_log_mutex);
                               lock(&fs_devs->device_list_mutex);
  lock(&type->i_mutex_dir_key#8);

 *** DEADLOCK ***

2 locks held by syz.0.17/4354:
 #0: ffffffff8c606608 (uuid_mutex){+.+.}-{3:3}, at: btrfs_forget_devices+0x1a/0x80 fs/btrfs/volumes.c:1430
 #1: ffff88805cef50e0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: btrfs_free_stale_devices+0x186/0xa60 fs/btrfs/volumes.c:603

stack backtrace:
CPU: 0 PID: 4354 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 check_noncircular+0x274/0x310 kernel/locking/lockdep.c:2133
 check_prev_add kernel/locking/lockdep.c:3053 [inline]
 check_prevs_add kernel/locking/lockdep.c:3172 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
 lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
 down_read+0x44/0x2e0 kernel/locking/rwsem.c:1498
 inode_lock_shared include/linux/fs.h:797 [inline]
 lookup_slow+0x46/0x70 fs/namei.c:1687
 walk_component+0x319/0x460 fs/namei.c:1984
 lookup_last fs/namei.c:2439 [inline]
 path_lookupat+0x169/0x440 fs/namei.c:2463
 filename_lookup+0x1e2/0x4f0 fs/namei.c:2492
 kern_path+0x37/0x190 fs/namei.c:2590
 lookup_bdev+0xbd/0x270 block/bdev.c:982
 device_matched fs/btrfs/volumes.c:568 [inline]
 btrfs_free_stale_devices+0x6db/0xa60 fs/btrfs/volumes.c:608
 btrfs_forget_devices+0x52/0x80 fs/btrfs/volumes.c:1431
 btrfs_control_ioctl+0x104/0x220 fs/btrfs/super.c:2450
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fc86d179749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe9a288268 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fc86d3cffa0 RCX: 00007fc86d179749
RDX: 0000200000000180 RSI: 0000000050009405 RDI: 0000000000000004
RBP: 00007fc86d1fdf91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc86d3cffa0 R14: 00007fc86d3cffa0 R15: 0000000000000003
 </TASK>