loop4: detected capacity change from 0 to 32768
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.4.750/7776 is trying to acquire lock:
ffff0000c09208e0 (&type->i_mutex_dir_key#2){++++}-{3:3}, at: inode_lock_shared include/linux/fs.h:768 [inline]
ffff0000c09208e0 (&type->i_mutex_dir_key#2){++++}-{3:3}, at: lookup_slow+0x50/0x84 fs/namei.c:1714

but task is already holding lock:
ffff0000d26448e0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: device_list_add+0x7d8/0x1c8c fs/btrfs/volumes.c:860

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+0x1a0/0x1f3c kernel/locking/mutex.c:603
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
       insert_dev_extents fs/btrfs/block-group.c:2520 [inline]
       btrfs_create_pending_block_groups+0x49c/0xe2c fs/btrfs/block-group.c:2571
       __btrfs_end_transaction+0x140/0x5fc fs/btrfs/transaction.c:1013
       btrfs_end_transaction+0x24/0x34 fs/btrfs/transaction.c:1052
       flush_space+0x87c/0xcdc fs/btrfs/space-info.c:816
       btrfs_async_reclaim_metadata_space+0x260/0x304 fs/btrfs/space-info.c:1126
       process_one_work+0x7e4/0x13bc kernel/workqueue.c:2292
       worker_thread+0x8cc/0xfe8 kernel/workqueue.c:2439
       kthread+0x254/0x2e0 kernel/kthread.c:376
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:850

-> #3 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x16c/0xb08 fs/btrfs/transaction.c:303
       start_transaction+0x794/0x1040 fs/btrfs/transaction.c:668
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:767
       btrfs_rebuild_free_space_tree+0xbc/0x6cc fs/btrfs/free-space-tree.c:1320
       btrfs_start_pre_rw_mount+0x2c8/0x664 fs/btrfs/disk-io.c:3215
       open_ctree+0x1ac4/0x229c fs/btrfs/disk-io.c:3812
       btrfs_fill_super+0x1d8/0x2fc fs/btrfs/super.c:1469
       btrfs_mount_root+0x79c/0x7ec fs/btrfs/super.c:1834
       legacy_get_tree+0xd8/0x174 fs/fs_context.c:632
       vfs_get_tree+0x90/0x278 fs/super.c:1573
       fc_mount fs/namespace.c:1048 [inline]
       vfs_kern_mount+0xdc/0x178 fs/namespace.c:1078
       btrfs_mount+0x2dc/0x974 fs/btrfs/super.c:1894
       legacy_get_tree+0xd8/0x174 fs/fs_context.c:632
       vfs_get_tree+0x90/0x278 fs/super.c:1573
       do_new_mount+0x228/0x804 fs/namespace.c:3078
       path_mount+0x5ac/0xe6c fs/namespace.c:3408
       do_mount fs/namespace.c:3421 [inline]
       __do_sys_mount fs/namespace.c:3629 [inline]
       __se_sys_mount fs/namespace.c:3606 [inline]
       __arm64_sys_mount+0x4a0/0x5a0 fs/namespace.c:3606
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #2 (btrfs_trans_num_writers){++++}-{0:0}:
       __lock_release kernel/locking/lockdep.c:5390 [inline]
       lock_release+0x308/0x90c kernel/locking/lockdep.c:5696
       percpu_up_read include/linux/percpu-rwsem.h:99 [inline]
       __sb_end_write include/linux/fs.h:1886 [inline]
       sb_end_intwrite+0x54/0x364 include/linux/fs.h:1942
       __btrfs_end_transaction+0x200/0x5fc fs/btrfs/transaction.c:1018
       btrfs_end_transaction+0x24/0x34 fs/btrfs/transaction.c:1052
       btrfs_dirty_inode+0x11c/0x1b8 fs/btrfs/inode.c:6340
       btrfs_update_time+0x170/0x18c fs/btrfs/inode.c:6375
       inode_update_time fs/inode.c:1958 [inline]
       touch_atime+0x368/0x7dc fs/inode.c:2031
       file_accessed include/linux/fs.h:2600 [inline]
       btrfs_file_mmap+0xb0/0x11c fs/btrfs/file.c:2045
       call_mmap include/linux/fs.h:2270 [inline]
       mmap_file+0x6c/0xc8 mm/util.c:1109
       __mmap_region mm/mmap.c:2772 [inline]
       mmap_region+0xc88/0x1860 mm/mmap.c:2916
       do_mmap+0xa64/0x1210 mm/mmap.c:1436
       vm_mmap_pgoff+0x194/0x298 mm/util.c:520
       ksys_mmap_pgoff+0x364/0x5a0 mm/mmap.c:1482
       __do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
       __se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
       __arm64_sys_mmap+0x108/0x120 arch/arm64/kernel/sys.c:21
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #1 (&mm->mmap_lock){++++}-{3:3}:
       __might_fault+0xc4/0x124 mm/memory.c:5850
       filldir64+0x2dc/0x930 fs/readdir.c:335
       dir_emit_dot include/linux/fs.h:3698 [inline]
       dir_emit_dots include/linux/fs.h:3709 [inline]
       dcache_readdir+0x144/0x638 fs/libfs.c:197
       iterate_dir+0x1f0/0x4d0 fs/readdir.c:-1
       __do_sys_getdents64 fs/readdir.c:369 [inline]
       __se_sys_getdents64 fs/readdir.c:354 [inline]
       __arm64_sys_getdents64+0x11c/0x314 fs/readdir.c:354
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #0 (&type->i_mutex_dir_key#2){++++}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3095 [inline]
       check_prevs_add kernel/locking/lockdep.c:3214 [inline]
       validate_chain kernel/locking/lockdep.c:3830 [inline]
       __lock_acquire+0x2808/0x6634 kernel/locking/lockdep.c:5063
       lock_acquire+0x20c/0x638 kernel/locking/lockdep.c:5676
       down_read+0x64/0x300 kernel/locking/rwsem.c:1520
       inode_lock_shared include/linux/fs.h:768 [inline]
       lookup_slow+0x50/0x84 fs/namei.c:1714
       walk_component+0x278/0x374 fs/namei.c:2006
       lookup_last fs/namei.c:2463 [inline]
       path_lookupat+0x168/0x3f0 fs/namei.c:2487
       filename_lookup+0x1d4/0x490 fs/namei.c:2516
       kern_path+0x48/0x6c fs/namei.c:2614
       is_same_device fs/btrfs/volumes.c:695 [inline]
       device_list_add+0x127c/0x1c8c fs/btrfs/volumes.c:928
       btrfs_scan_one_device+0x368/0x558 fs/btrfs/volumes.c:1461
       btrfs_mount_root+0x470/0x7ec fs/btrfs/super.c:1796
       legacy_get_tree+0xd8/0x174 fs/fs_context.c:632
       vfs_get_tree+0x90/0x278 fs/super.c:1573
       fc_mount fs/namespace.c:1048 [inline]
       vfs_kern_mount+0xdc/0x178 fs/namespace.c:1078
       btrfs_mount+0x2dc/0x974 fs/btrfs/super.c:1894
       legacy_get_tree+0xd8/0x174 fs/fs_context.c:632
       vfs_get_tree+0x90/0x278 fs/super.c:1573
       do_new_mount+0x228/0x804 fs/namespace.c:3078
       path_mount+0x5ac/0xe6c fs/namespace.c:3408
       do_mount fs/namespace.c:3421 [inline]
       __do_sys_mount fs/namespace.c:3629 [inline]
       __se_sys_mount fs/namespace.c:3606 [inline]
       __arm64_sys_mount+0x4a0/0x5a0 fs/namespace.c:3606
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

other info that might help us debug this:

Chain exists of:
  &type->i_mutex_dir_key#2 --> btrfs_trans_num_extwriters --> &fs_devs->device_list_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&fs_devs->device_list_mutex);
                               lock(btrfs_trans_num_extwriters);
                               lock(&fs_devs->device_list_mutex);
  lock(&type->i_mutex_dir_key#2);

 *** DEADLOCK ***

2 locks held by syz.4.750/7776:
 #0: ffff800015aa6a48 (uuid_mutex){+.+.}-{3:3}, at: btrfs_mount_root+0x1fc/0x7ec fs/btrfs/super.c:1789
 #1: ffff0000d26448e0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: device_list_add+0x7d8/0x1c8c fs/btrfs/volumes.c:860

stack backtrace:
CPU: 1 PID: 7776 Comm: syz.4.750 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
Call trace:
 dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
 dump_stack+0x1c/0x5c lib/dump_stack.c:113
 print_circular_bug+0x148/0x1b0 kernel/locking/lockdep.c:2048
 check_noncircular+0x264/0x2f8 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3095 [inline]
 check_prevs_add kernel/locking/lockdep.c:3214 [inline]
 validate_chain kernel/locking/lockdep.c:3830 [inline]
 __lock_acquire+0x2808/0x6634 kernel/locking/lockdep.c:5063
 lock_acquire+0x20c/0x638 kernel/locking/lockdep.c:5676
 down_read+0x64/0x300 kernel/locking/rwsem.c:1520
 inode_lock_shared include/linux/fs.h:768 [inline]
 lookup_slow+0x50/0x84 fs/namei.c:1714
 walk_component+0x278/0x374 fs/namei.c:2006
 lookup_last fs/namei.c:2463 [inline]
 path_lookupat+0x168/0x3f0 fs/namei.c:2487
 filename_lookup+0x1d4/0x490 fs/namei.c:2516
 kern_path+0x48/0x6c fs/namei.c:2614
 is_same_device fs/btrfs/volumes.c:695 [inline]
 device_list_add+0x127c/0x1c8c fs/btrfs/volumes.c:928
 btrfs_scan_one_device+0x368/0x558 fs/btrfs/volumes.c:1461
 btrfs_mount_root+0x470/0x7ec fs/btrfs/super.c:1796
 legacy_get_tree+0xd8/0x174 fs/fs_context.c:632
 vfs_get_tree+0x90/0x278 fs/super.c:1573
 fc_mount fs/namespace.c:1048 [inline]
 vfs_kern_mount+0xdc/0x178 fs/namespace.c:1078
 btrfs_mount+0x2dc/0x974 fs/btrfs/super.c:1894
 legacy_get_tree+0xd8/0x174 fs/fs_context.c:632
 vfs_get_tree+0x90/0x278 fs/super.c:1573
 do_new_mount+0x228/0x804 fs/namespace.c:3078
 path_mount+0x5ac/0xe6c fs/namespace.c:3408
 do_mount fs/namespace.c:3421 [inline]
 __do_sys_mount fs/namespace.c:3629 [inline]
 __se_sys_mount fs/namespace.c:3606 [inline]
 __arm64_sys_mount+0x4a0/0x5a0 fs/namespace.c:3606
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
BTRFS info (device loop4): first mount of filesystem c9fe44da-de57-406a-8241-57ec7d4412cf
BTRFS info (device loop4): using crc32c (crc32c-generic) checksum algorithm
BTRFS info (device loop4): setting nodatasum
BTRFS info (device loop4): force zlib compression, level 3
BTRFS info (device loop4): setting incompat feature flag for COMPRESS_LZO (0x8)
BTRFS info (device loop4): use lzo compression, level 0
BTRFS info (device loop4): turning on flush-on-commit
BTRFS info (device loop4): enabling auto defrag
BTRFS info (device loop4): max_inline at 0
BTRFS info (device loop4): using free space tree
BTRFS info (device loop4): enabling ssd optimizations