syzbot

BTRFS info (device loop4): enabling ssd optimizations
BTRFS info (device loop4): enabling free space tree
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.4.228/7419 is trying to acquire lock:
ffff88801988c238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x41/0x520 fs/kernfs/dir.c:791

but task is already holding lock:
ffff888053562198 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}, at: btrfs_quota_enable+0x202/0x2600 fs/btrfs/qgroup.c:1018

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&fs_info->qgroup_ioctl_lock){+.+.}-{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
       btrfs_create_qgroup+0x55/0x520 fs/btrfs/qgroup.c:1666
       create_pending_snapshot+0x6b4/0x3280 fs/btrfs/transaction.c:1736
       create_pending_snapshots+0x17c/0x1c0 fs/btrfs/transaction.c:1927
       btrfs_commit_transaction+0xeea/0x3950 fs/btrfs/transaction.c:2415
       create_snapshot+0x6bc/0xba0 fs/btrfs/ioctl.c:782
       btrfs_mksubvol+0x545/0x6d0 fs/btrfs/ioctl.c:934
       btrfs_mksnapshot+0xab/0xf0 fs/btrfs/ioctl.c:978
       __btrfs_ioctl_snap_create+0x526/0x740 fs/btrfs/ioctl.c:1242
       btrfs_ioctl_snap_create_v2+0x1fb/0x3b0 fs/btrfs/ioctl.c:1322
       btrfs_ioctl+0xa65/0xd00 fs/btrfs/ioctl.c:-1
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&fs_info->reloc_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
       btrfs_record_root_in_trans+0x14f/0x180 fs/btrfs/transaction.c:503
       start_transaction+0x3a4/0x1620 fs/btrfs/transaction.c:779
       create_snapshot+0x52b/0xba0 fs/btrfs/ioctl.c:767
       btrfs_mksubvol+0x545/0x6d0 fs/btrfs/ioctl.c:934
       btrfs_mksnapshot+0xab/0xf0 fs/btrfs/ioctl.c:978
       __btrfs_ioctl_snap_create+0x526/0x740 fs/btrfs/ioctl.c:1242
       btrfs_ioctl_snap_create_v2+0x1fb/0x3b0 fs/btrfs/ioctl.c:1322
       btrfs_ioctl+0xa65/0xd00 fs/btrfs/ioctl.c:-1
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #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/0x760 fs/btrfs/free-space-tree.c:1339
       btrfs_start_pre_rw_mount+0x128f/0x1bf0 fs/btrfs/disk-io.c:3075
       open_ctree+0x293a/0x3a10 fs/btrfs/disk-io.c:3617
       btrfs_fill_super fs/btrfs/super.c:980 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1943 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2080 [inline]
       btrfs_get_tree+0xf55/0x1820 fs/btrfs/super.c:2114
       vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
       do_new_mount+0x2a2/0x9e0 fs/namespace.c:3808
       do_mount fs/namespace.c:4136 [inline]
       __do_sys_mount fs/namespace.c:4347 [inline]
       __se_sys_mount+0x317/0x410 fs/namespace.c:4324
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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:1794 [inline]
       sb_end_intwrite+0x26/0x1c0 include/linux/fs.h:1911
       __btrfs_end_transaction+0x248/0x640 fs/btrfs/transaction.c:1076
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6258
       inode_update_time fs/inode.c:2075 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2148
       file_accessed include/linux/fs.h:2664 [inline]
       btrfs_file_mmap_prepare+0xde/0x150 fs/btrfs/file.c:2050
       vfs_mmap_prepare include/linux/fs.h:2295 [inline]
       call_mmap_prepare mm/vma.c:2585 [inline]
       __mmap_region mm/vma.c:2653 [inline]
       mmap_region+0xb49/0x20a0 mm/vma.c:2739
       do_mmap+0xc23/0x10c0 mm/mmap.c:558
       vm_mmap_pgoff+0x2a9/0x4d0 mm/util.c:580
       ksys_mmap_pgoff+0x4e9/0x720 mm/mmap.c:604
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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:462
       get_mmap_lock_carefully mm/mmap_lock.c:286 [inline]
       lock_mm_and_find_vma+0x2a8/0x300 mm/mmap_lock.c:337
       do_user_addr_fault+0x331/0x1390 arch/x86/mm/fault.c:1359
       handle_page_fault arch/x86/mm/fault.c:1476 [inline]
       exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
       user_access_begin arch/x86/include/asm/uaccess.h:-1 [inline]
       filldir+0x2a2/0x6c0 fs/readdir.c:290
       dir_emit include/linux/fs.h:3959 [inline]
       kernfs_fop_readdir+0x537/0x870 fs/kernfs/dir.c:1910
       iterate_dir+0x3a2/0x580 fs/readdir.c:108
       __do_sys_getdents fs/readdir.c:326 [inline]
       __se_sys_getdents+0xe4/0x250 fs/readdir.c:312
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_rwsem){++++}-{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_write+0x3a/0x50 kernel/locking/rwsem.c:1590
       kernfs_add_one+0x41/0x520 fs/kernfs/dir.c:791
       kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1093
       sysfs_create_dir_ns+0x123/0x280 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x5a5/0xb50 lib/kobject.c:240
       kobject_add_varg lib/kobject.c:374 [inline]
       kobject_init_and_add+0x125/0x190 lib/kobject.c:457
       btrfs_sysfs_add_qgroups+0x111/0x2b0 fs/btrfs/sysfs.c:2641
       btrfs_quota_enable+0x253/0x2600 fs/btrfs/qgroup.c:1022
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3667
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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:
  &root->kernfs_rwsem --> &fs_info->reloc_mutex --> &fs_info->qgroup_ioctl_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&fs_info->qgroup_ioctl_lock);
                               lock(&fs_info->reloc_mutex);
                               lock(&fs_info->qgroup_ioctl_lock);
  lock(&root->kernfs_rwsem);

 *** DEADLOCK ***

3 locks held by syz.4.228/7419:
 #0: ffff88802fe24488 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write_file+0x63/0x210 fs/namespace.c:601
 #1: ffff888053561060 (&fs_info->subvol_sem){++++}-{4:4}, at: btrfs_ioctl_quota_ctl+0x17b/0x1c0 fs/btrfs/ioctl.c:3666
 #2: ffff888053562198 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}, at: btrfs_quota_enable+0x202/0x2600 fs/btrfs/qgroup.c:1018

stack backtrace:
CPU: 1 UID: 0 PID: 7419 Comm: syz.4.228 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
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_write+0x3a/0x50 kernel/locking/rwsem.c:1590
 kernfs_add_one+0x41/0x520 fs/kernfs/dir.c:791
 kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1093
 sysfs_create_dir_ns+0x123/0x280 fs/sysfs/dir.c:59
 create_dir lib/kobject.c:73 [inline]
 kobject_add_internal+0x5a5/0xb50 lib/kobject.c:240
 kobject_add_varg lib/kobject.c:374 [inline]
 kobject_init_and_add+0x125/0x190 lib/kobject.c:457
 btrfs_sysfs_add_qgroups+0x111/0x2b0 fs/btrfs/sysfs.c:2641
 btrfs_quota_enable+0x253/0x2600 fs/btrfs/qgroup.c:1022
 btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3667
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa5d266eba9
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:00007fa5d08d6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fa5d28b5fa0 RCX: 00007fa5d266eba9
RDX: 00002000000000c0 RSI: 00000000c0109428 RDI: 0000000000000003
RBP: 00007fa5d26f1e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa5d28b6038 R14: 00007fa5d28b5fa0 R15: 00007fff49911a48
 </TASK>