======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.7.1467/10495 is trying to acquire lock:
ffff888062c75a60 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}, at: btrfs_quota_enable+0x2b1/0x1e20 fs/btrfs/qgroup.c:1061

but task is already holding lock:
ffff888062c766a8 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x6b2/0xd40 fs/btrfs/transaction.c:299

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x18a/0xd40 fs/btrfs/transaction.c:324
       start_transaction+0x6ed/0x17d0 fs/btrfs/transaction.c:729
       btrfs_rebuild_free_space_tree+0xbb/0x4f0 fs/btrfs/free-space-tree.c:1345
       btrfs_start_pre_rw_mount+0x15b8/0x2030 fs/btrfs/disk-io.c:3086
       open_ctree+0x2de0/0x4190 fs/btrfs/disk-io.c:3767
       btrfs_fill_super fs/btrfs/super.c:974 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1969 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2112 [inline]
       btrfs_get_tree+0x1084/0x1980 fs/btrfs/super.c:2146
       vfs_get_tree+0x92/0x2a0 fs/super.c:1933
       fc_mount fs/namespace.c:1198 [inline]
       do_new_mount_fc fs/namespace.c:3772 [inline]
       do_new_mount+0x319/0xdc0 fs/namespace.c:3848
       do_mount fs/namespace.c:4181 [inline]
       __do_sys_mount fs/namespace.c:4397 [inline]
       __se_sys_mount+0x31d/0x420 fs/namespace.c:4374
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (btrfs_trans_num_writers){++++}-{0:0}:
       __lock_release kernel/locking/lockdep.c:5627 [inline]
       lock_release+0x1a3/0x3c0 kernel/locking/lockdep.c:5964
       percpu_up_read include/linux/percpu-rwsem.h:114 [inline]
       __sb_end_write include/linux/fs/super.h:14 [inline]
       sb_end_intwrite+0x26/0x190 include/linux/fs/super.h:101
       __btrfs_end_transaction+0x23f/0x640 fs/btrfs/transaction.c:1106
       btrfs_dirty_inode+0x108/0x190 fs/btrfs/inode.c:6472
       touch_atime+0x2f8/0x670 fs/inode.c:2326
       file_accessed include/linux/fs.h:2277 [inline]
       btrfs_file_mmap_prepare+0x172/0x1f0 fs/btrfs/file.c:2003
       vfs_mmap_prepare include/linux/fs.h:2069 [inline]
       call_mmap_prepare mm/vma.c:2784 [inline]
       __mmap_region mm/vma.c:2873 [inline]
       mmap_region+0xe7e/0x2270 mm/vma.c:2974
       do_mmap+0xe0a/0x1300 mm/mmap.c:573
       vm_mmap_pgoff+0x272/0x4e0 mm/util.c:581
       ksys_mmap_pgoff+0x4dc/0x760 mm/mmap.c:619
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&mm->mmap_lock){++++}-{4:4}:
       down_read_killable+0x50/0x3b0 kernel/locking/rwsem.c:1599
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:609
       get_mmap_lock_carefully mm/mmap_lock.c:450 [inline]
       lock_mm_and_find_vma+0x2d6/0x340 mm/mmap_lock.c:501
       do_user_addr_fault+0x343/0x1340 arch/x86/mm/fault.c:1366
       handle_page_fault arch/x86/mm/fault.c:1483 [inline]
       exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
       filldir+0x2bd/0x630 fs/readdir.c:-1
       dir_emit include/linux/fs.h:3607 [inline]
       kernfs_fop_readdir+0x580/0x960 fs/kernfs/dir.c:1999
       iterate_dir+0x2e2/0x4d0 fs/readdir.c:110
       __do_sys_getdents fs/readdir.c:319 [inline]
       __se_sys_getdents+0xf1/0x270 fs/readdir.c:304
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&root->kernfs_rwsem){++++}-{4:4}:
       down_write+0x96/0x200 kernel/locking/rwsem.c:1631
       kernfs_add_one+0x41/0x6f0 fs/kernfs/dir.c:825
       kernfs_create_dir_ns+0x1a1/0x230 fs/kernfs/dir.c:1130
       sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x622/0xcd0 lib/kobject.c:240
       kobject_add_varg lib/kobject.c:374 [inline]
       kobject_init_and_add+0x12b/0x1a0 lib/kobject.c:457
       btrfs_sysfs_add_qgroups+0x118/0x2f0 fs/btrfs/sysfs.c:2604
       btrfs_quota_enable+0x274/0x1e20 fs/btrfs/qgroup.c:1032
       btrfs_ioctl_quota_ctl+0x186/0x1f0 fs/btrfs/ioctl.c:3581
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3209 [inline]
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
       lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       btrfs_quota_enable+0x2b1/0x1e20 fs/btrfs/qgroup.c:1061
       btrfs_ioctl_quota_ctl+0x186/0x1f0 fs/btrfs/ioctl.c:3581
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &fs_info->qgroup_ioctl_lock --> btrfs_trans_num_writers --> btrfs_trans_num_extwriters

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(btrfs_trans_num_extwriters);
                               lock(btrfs_trans_num_writers);
                               lock(btrfs_trans_num_extwriters);
  lock(&fs_info->qgroup_ioctl_lock);

 *** DEADLOCK ***

locks held by syz.7.1467/10495: 5, last CPU#1:
 #0: ffff88807b972460 (sb_writers#37){.+.+}-{0:0}, at: mnt_want_write_file+0x60/0x200 fs/namespace.c:538
 #1: ffff888062c74d18 (&fs_info->subvol_sem){+.+.}-{4:4}, at: btrfs_ioctl_quota_ctl+0x17b/0x1f0 fs/btrfs/ioctl.c:3580
 #2: ffff88807b972650 (sb_internal#4){.+.+}-{0:0}, at: btrfs_quota_enable+0x2a4/0x1e20 fs/btrfs/qgroup.c:1059
 #3: ffff888062c76680 (btrfs_trans_num_writers){++++}-{0:0}, at: join_transaction+0x6b2/0xd40 fs/btrfs/transaction.c:299
 #4: ffff888062c766a8 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x6b2/0xd40 fs/btrfs/transaction.c:299

stack backtrace:
CPU: 1 UID: 0 PID: 10495 Comm: syz.7.1467 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
 check_prev_add kernel/locking/lockdep.c:3209 [inline]
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
 btrfs_quota_enable+0x2b1/0x1e20 fs/btrfs/qgroup.c:1061
 btrfs_ioctl_quota_ctl+0x186/0x1f0 fs/btrfs/ioctl.c:3581
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6b1939e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f6b1a1ba028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f6b19625fa0 RCX: 00007f6b1939e159
RDX: 0000200000000580 RSI: 00000000c0109428 RDI: 0000000000000003
RBP: 00007f6b1943506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6b19626038 R14: 00007f6b19625fa0 R15: 00007ffe8e3eeaa8
 </TASK>