loop6: detected capacity change from 0 to 32768
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.6.1104/14243 is trying to acquire lock:
ffff88805f35e598 (&type->i_mutex_dir_key#5){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:1043 [inline]
ffff88805f35e598 (&type->i_mutex_dir_key#5){++++}-{4:4}, at: lookup_slow+0x46/0x70 fs/namei.c:1932

but task is already holding lock:
ffff888036e018c8 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x487/0x2280 fs/btrfs/volumes.c:842

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:533 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552
       insert_dev_extents fs/btrfs/block-group.c:2838 [inline]
       btrfs_create_pending_block_groups+0x77b/0x1b40 fs/btrfs/block-group.c:2889
       __btrfs_end_transaction+0x140/0x640 fs/btrfs/transaction.c:1080
       flush_space+0x35e/0xd80 fs/btrfs/space-info.c:900
       do_async_reclaim_metadata_space+0x411/0x970 fs/btrfs/space-info.c:1187
       btrfs_async_reclaim_metadata_space+0x89/0xe0 fs/btrfs/space-info.c:1254
       process_one_work kernel/workqueue.c:3276 [inline]
       process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
       worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
       kthread+0x388/0x470 kernel/kthread.c:436
       ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #3 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x1a4/0xc90 fs/btrfs/transaction.c:323
       start_transaction+0x6b9/0x1650 fs/btrfs/transaction.c:708
       btrfs_rebuild_free_space_tree+0xbb/0x6e0 fs/btrfs/free-space-tree.c:1335
       btrfs_start_pre_rw_mount+0x1529/0x1f20 fs/btrfs/disk-io.c:3071
       open_ctree+0x2e07/0x4220 fs/btrfs/disk-io.c:3668
       btrfs_fill_super fs/btrfs/super.c:981 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1944 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2087 [inline]
       btrfs_get_tree+0x1061/0x1930 fs/btrfs/super.c:2121
       vfs_get_tree+0x92/0x2a0 fs/super.c:1754
       fc_mount fs/namespace.c:1193 [inline]
       do_new_mount_fc fs/namespace.c:3763 [inline]
       do_new_mount+0x341/0xd30 fs/namespace.c:3839
       do_mount fs/namespace.c:4172 [inline]
       __do_sys_mount fs/namespace.c:4361 [inline]
       __se_sys_mount+0x31d/0x420 fs/namespace.c:4338
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_writers){++++}-{0:0}:
       __lock_release kernel/locking/lockdep.c:5574 [inline]
       lock_release+0x199/0x3d0 kernel/locking/lockdep.c:5889
       percpu_up_read include/linux/percpu-rwsem.h:112 [inline]
       __sb_end_write include/linux/fs/super.h:14 [inline]
       sb_end_intwrite+0x26/0x1c0 include/linux/fs/super.h:101
       __btrfs_end_transaction+0x248/0x640 fs/btrfs/transaction.c:1085
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6457
       touch_atime+0x2f8/0x6b0 fs/inode.c:2271
       file_accessed include/linux/fs.h:2263 [inline]
       btrfs_file_mmap_prepare+0x189/0x200 fs/btrfs/file.c:2051
       vfs_mmap_prepare include/linux/fs.h:2075 [inline]
       call_mmap_prepare mm/vma.c:2644 [inline]
       __mmap_region mm/vma.c:2743 [inline]
       mmap_region+0xdf2/0x2190 mm/vma.c:2844
       do_mmap+0xc2f/0x10c0 mm/mmap.c:559
       vm_mmap_pgoff+0x2cc/0x4f0 mm/util.c:581
       ksys_mmap_pgoff+0x4e8/0x720 mm/mmap.c:605
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&mm->mmap_lock){++++}-{4:4}:
       down_read_killable+0xa4/0x220 kernel/locking/rwsem.c:1560
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:601
       get_mmap_lock_carefully mm/mmap_lock.c:450 [inline]
       lock_mm_and_find_vma+0x2d7/0x340 mm/mmap_lock.c:501
       do_user_addr_fault+0x330/0x1340 arch/x86/mm/fault.c:1357
       handle_page_fault arch/x86/mm/fault.c:1474 [inline]
       exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
       filldir+0x2b5/0x690 fs/readdir.c:295
       dir_emit include/linux/fs.h:3566 [inline]
       offset_dir_emit fs/libfs.c:500 [inline]
       offset_iterate_dir fs/libfs.c:516 [inline]
       offset_readdir+0x3fc/0x530 fs/libfs.c:565
       iterate_dir+0x3a5/0x580 fs/readdir.c:108
       __do_sys_getdents fs/readdir.c:327 [inline]
       __se_sys_getdents+0xf1/0x270 fs/readdir.c:312
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&type->i_mutex_dir_key#5){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
       down_read+0x97/0x200 kernel/locking/rwsem.c:1537
       inode_lock_shared include/linux/fs.h:1043 [inline]
       lookup_slow+0x46/0x70 fs/namei.c:1932
       walk_component fs/namei.c:2279 [inline]
       lookup_last fs/namei.c:2786 [inline]
       path_lookupat+0x3f5/0x8c0 fs/namei.c:2810
       filename_lookup+0x256/0x5d0 fs/namei.c:2839
       kern_path+0x3d/0x150 fs/namei.c:3046
       is_same_device fs/btrfs/volumes.c:763 [inline]
       device_list_add+0xfd1/0x2280 fs/btrfs/volumes.c:897
       btrfs_scan_one_device+0x3ef/0x680 fs/btrfs/volumes.c:1498
       btrfs_get_tree_super fs/btrfs/super.c:1858 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2087 [inline]
       btrfs_get_tree+0x4ab/0x1930 fs/btrfs/super.c:2121
       vfs_get_tree+0x92/0x2a0 fs/super.c:1754
       fc_mount fs/namespace.c:1193 [inline]
       do_new_mount_fc fs/namespace.c:3763 [inline]
       do_new_mount+0x341/0xd30 fs/namespace.c:3839
       do_mount fs/namespace.c:4172 [inline]
       __do_sys_mount fs/namespace.c:4361 [inline]
       __se_sys_mount+0x31d/0x420 fs/namespace.c:4338
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &type->i_mutex_dir_key#5 --> 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);
  rlock(&type->i_mutex_dir_key#5);

 *** DEADLOCK ***

2 locks held by syz.6.1104/14243:
 #0: ffffffff8e3d9cb8 (uuid_mutex){+.+.}-{4:4}, at: btrfs_get_tree_super fs/btrfs/super.c:1852 [inline]
 #0: ffffffff8e3d9cb8 (uuid_mutex){+.+.}-{4:4}, at: btrfs_get_tree_subvol fs/btrfs/super.c:2087 [inline]
 #0: ffffffff8e3d9cb8 (uuid_mutex){+.+.}-{4:4}, at: btrfs_get_tree+0x47c/0x1930 fs/btrfs/super.c:2121
 #1: ffff888036e018c8 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x487/0x2280 fs/btrfs/volumes.c:842

stack backtrace:
CPU: 1 UID: 0 PID: 14243 Comm: syz.6.1104 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
 down_read+0x97/0x200 kernel/locking/rwsem.c:1537
 inode_lock_shared include/linux/fs.h:1043 [inline]
 lookup_slow+0x46/0x70 fs/namei.c:1932
 walk_component fs/namei.c:2279 [inline]
 lookup_last fs/namei.c:2786 [inline]
 path_lookupat+0x3f5/0x8c0 fs/namei.c:2810
 filename_lookup+0x256/0x5d0 fs/namei.c:2839
 kern_path+0x3d/0x150 fs/namei.c:3046
 is_same_device fs/btrfs/volumes.c:763 [inline]
 device_list_add+0xfd1/0x2280 fs/btrfs/volumes.c:897
 btrfs_scan_one_device+0x3ef/0x680 fs/btrfs/volumes.c:1498
 btrfs_get_tree_super fs/btrfs/super.c:1858 [inline]
 btrfs_get_tree_subvol fs/btrfs/super.c:2087 [inline]
 btrfs_get_tree+0x4ab/0x1930 fs/btrfs/super.c:2121
 vfs_get_tree+0x92/0x2a0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3763 [inline]
 do_new_mount+0x341/0xd30 fs/namespace.c:3839
 do_mount fs/namespace.c:4172 [inline]
 __do_sys_mount fs/namespace.c:4361 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4338
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc0891eda8a
Code: 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc087445e58 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fc087445ee0 RCX: 00007fc0891eda8a
RDX: 0000200000000200 RSI: 0000200000005600 RDI: 00007fc087445ea0
RBP: 0000200000000200 R08: 00007fc087445ee0 R09: 0000000000000800
R10: 0000000000000800 R11: 0000000000000246 R12: 0000200000005600
R13: 00007fc087445ea0 R14: 000000000000559e R15: 0000200000000240
 </TASK>
BTRFS info (device loop6): first mount of filesystem 395ef67a-297e-477c-816d-cd80a5b93e5d
BTRFS info (device loop6): using sha256 checksum algorithm
BTRFS info (device loop6): enabling ssd optimizations
BTRFS info (device loop6): turning on async discard
BTRFS info (device loop6): enabling free space tree
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