syzbot

loop8: detected capacity change from 0 to 32768
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.8.845/12516 is trying to acquire lock:
ffff888057a83cf8 (&type->i_mutex_dir_key#5){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:995 [inline]
ffff888057a83cf8 (&type->i_mutex_dir_key#5){++++}-{4:4}, at: lookup_slow+0x46/0x70 fs/namei.c:1832

but task is already holding lock:
ffff88805f11f4c8 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x595/0x22a0 fs/btrfs/volumes.c:839

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/rtmutex_api.c:535 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:547
       insert_dev_extents fs/btrfs/block-group.c:2754 [inline]
       btrfs_create_pending_block_groups+0x5f8/0x1780 fs/btrfs/block-group.c:2805
       __btrfs_end_transaction+0x140/0x640 fs/btrfs/transaction.c:1071
       flush_space+0x315/0xcd0 fs/btrfs/space-info.c:865
       do_async_reclaim_data_space+0x11c/0x520 fs/btrfs/space-info.c:1394
       btrfs_async_reclaim_data_space+0x41/0x90 fs/btrfs/space-info.c:1458
       process_one_work kernel/workqueue.c:3263 [inline]
       process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
       worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
       kthread+0x711/0x8a0 kernel/kthread.c:463
       ret_from_fork+0x4bc/0x870 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}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       join_transaction+0x1a4/0xca0 fs/btrfs/transaction.c:321
       start_transaction+0x6b6/0x1620 fs/btrfs/transaction.c:705
       btrfs_rebuild_free_space_tree+0xad/0x6d0 fs/btrfs/free-space-tree.c:1339
       btrfs_start_pre_rw_mount+0x128f/0x1bf0 fs/btrfs/disk-io.c:3062
       open_ctree+0x2b11/0x3d20 fs/btrfs/disk-io.c:3619
       btrfs_fill_super fs/btrfs/super.c:987 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1952 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2089 [inline]
       btrfs_get_tree+0xf5a/0x1830 fs/btrfs/super.c:2123
       vfs_get_tree+0x92/0x2b0 fs/super.c:1751
       fc_mount fs/namespace.c:1208 [inline]
       do_new_mount_fc fs/namespace.c:3651 [inline]
       do_new_mount+0x302/0xa10 fs/namespace.c:3727
       do_mount fs/namespace.c:4050 [inline]
       __do_sys_mount fs/namespace.c:4238 [inline]
       __se_sys_mount+0x313/0x410 fs/namespace.c:4215
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_writers){++++}-{0:0}:
       reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385
       __lock_release kernel/locking/lockdep.c:5574 [inline]
       lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889
       percpu_up_read include/linux/percpu-rwsem.h:112 [inline]
       __sb_end_write include/linux/fs.h:1911 [inline]
       sb_end_intwrite+0x26/0x1c0 include/linux/fs.h:2028
       __btrfs_end_transaction+0x248/0x640 fs/btrfs/transaction.c:1076
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6284
       inode_update_time fs/inode.c:2117 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2190
       file_accessed include/linux/fs.h:2673 [inline]
       btrfs_file_mmap_prepare+0xde/0x150 fs/btrfs/file.c:2049
       vfs_mmap_prepare include/linux/fs.h:2410 [inline]
       call_mmap_prepare mm/vma.c:2586 [inline]
       __mmap_region mm/vma.c:2654 [inline]
       mmap_region+0xb52/0x20f0 mm/vma.c:2740
       do_mmap+0xc23/0x10c0 mm/mmap.c:558
       vm_mmap_pgoff+0x2a9/0x4d0 mm/util.c:581
       ksys_mmap_pgoff+0x4e9/0x720 mm/mmap.c:604
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&mm->mmap_lock){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       down_read_killable+0x9d/0x220 kernel/locking/rwsem.c:1560
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:377
       get_mmap_lock_carefully mm/mmap_lock.c:377 [inline]
       lock_mm_and_find_vma+0x2a8/0x300 mm/mmap_lock.c:428
       do_user_addr_fault+0x331/0x1380 arch/x86/mm/fault.c:1359
       handle_page_fault arch/x86/mm/fault.c:1476 [inline]
       exc_page_fault+0x82/0x100 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
       filldir64+0x2ce/0x690 fs/readdir.c:-1
       dir_emit include/linux/fs.h:3986 [inline]
       offset_dir_emit fs/libfs.c:507 [inline]
       offset_iterate_dir fs/libfs.c:523 [inline]
       offset_readdir+0x44c/0x560 fs/libfs.c:572
       iterate_dir+0x3a5/0x580 fs/readdir.c:108
       __do_sys_getdents64 fs/readdir.c:410 [inline]
       __se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       down_read+0x97/0x1f0 kernel/locking/rwsem.c:1537
       inode_lock_shared include/linux/fs.h:995 [inline]
       lookup_slow+0x46/0x70 fs/namei.c:1832
       walk_component+0x2d2/0x400 fs/namei.c:2151
       lookup_last fs/namei.c:2652 [inline]
       path_lookupat+0x163/0x430 fs/namei.c:2676
       filename_lookup+0x212/0x570 fs/namei.c:2705
       kern_path+0x35/0x50 fs/namei.c:2863
       is_same_device fs/btrfs/volumes.c:759 [inline]
       device_list_add+0xe2a/0x22a0 fs/btrfs/volumes.c:894
       btrfs_scan_one_device+0x3ee/0x650 fs/btrfs/volumes.c:1493
       btrfs_get_tree_super fs/btrfs/super.c:1865 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2089 [inline]
       btrfs_get_tree+0x438/0x1830 fs/btrfs/super.c:2123
       vfs_get_tree+0x92/0x2b0 fs/super.c:1751
       fc_mount fs/namespace.c:1208 [inline]
       do_new_mount_fc fs/namespace.c:3651 [inline]
       do_new_mount+0x302/0xa10 fs/namespace.c:3727
       do_mount fs/namespace.c:4050 [inline]
       __do_sys_mount fs/namespace.c:4238 [inline]
       __se_sys_mount+0x313/0x410 fs/namespace.c:4215
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 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.8.845/12516:
 #0: ffffffff8dd592b8 (uuid_mutex){+.+.}-{4:4}, at: btrfs_get_tree_super fs/btrfs/super.c:1859 [inline]
 #0: ffffffff8dd592b8 (uuid_mutex){+.+.}-{4:4}, at: btrfs_get_tree_subvol fs/btrfs/super.c:2089 [inline]
 #0: ffffffff8dd592b8 (uuid_mutex){+.+.}-{4:4}, at: btrfs_get_tree+0x40d/0x1830 fs/btrfs/super.c:2123
 #1: ffff88805f11f4c8 (&fs_devs->device_list_mutex){+.+.}-{4:4}, at: device_list_add+0x595/0x22a0 fs/btrfs/volumes.c:839

stack backtrace:
CPU: 0 UID: 0 PID: 12516 Comm: syz.8.845 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 down_read+0x97/0x1f0 kernel/locking/rwsem.c:1537
 inode_lock_shared include/linux/fs.h:995 [inline]
 lookup_slow+0x46/0x70 fs/namei.c:1832
 walk_component+0x2d2/0x400 fs/namei.c:2151
 lookup_last fs/namei.c:2652 [inline]
 path_lookupat+0x163/0x430 fs/namei.c:2676
 filename_lookup+0x212/0x570 fs/namei.c:2705
 kern_path+0x35/0x50 fs/namei.c:2863
 is_same_device fs/btrfs/volumes.c:759 [inline]
 device_list_add+0xe2a/0x22a0 fs/btrfs/volumes.c:894
 btrfs_scan_one_device+0x3ee/0x650 fs/btrfs/volumes.c:1493
 btrfs_get_tree_super fs/btrfs/super.c:1865 [inline]
 btrfs_get_tree_subvol fs/btrfs/super.c:2089 [inline]
 btrfs_get_tree+0x438/0x1830 fs/btrfs/super.c:2123
 vfs_get_tree+0x92/0x2b0 fs/super.c:1751
 fc_mount fs/namespace.c:1208 [inline]
 do_new_mount_fc fs/namespace.c:3651 [inline]
 do_new_mount+0x302/0xa10 fs/namespace.c:3727
 do_mount fs/namespace.c:4050 [inline]
 __do_sys_mount fs/namespace.c:4238 [inline]
 __se_sys_mount+0x313/0x410 fs/namespace.c:4215
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f75e21e066a
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f75e043de68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f75e043def0 RCX: 00007f75e21e066a
RDX: 0000200000000200 RSI: 0000200000005600 RDI: 00007f75e043deb0
RBP: 0000200000000200 R08: 00007f75e043def0 R09: 0000000000000800
R10: 0000000000000800 R11: 0000000000000246 R12: 0000200000005600
R13: 00007f75e043deb0 R14: 000000000000559e R15: 0000200000000240
 </TASK>
BTRFS info (device loop8): first mount of filesystem 395ef67a-297e-477c-816d-cd80a5b93e5d
BTRFS info (device loop8): using sha256 (sha256-lib) checksum algorithm
BTRFS info (device loop8): enabling ssd optimizations
BTRFS info (device loop8): enabling free space tree