syzbot

BTRFS info (device loop0): clearing compat-ro feature flag for FREE_SPACE_TREE (0x1)
BTRFS info (device loop0): clearing compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)
======================================================
WARNING: possible circular locking dependency detected
6.15.0-rc6-syzkaller-00085-gc94d59a126cb #0 Not tainted
------------------------------------------------------
syz.0.60/6428 is trying to acquire lock:
ffff888059e69918 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}, at: btrfs_quota_enable+0x2be/0x1d50 fs/btrfs/qgroup.c:1059

but task is already holding lock:
ffff888059e6a4f8 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x164/0xd70 fs/btrfs/transaction.c:320

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (btrfs_trans_num_extwriters){++++}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
       join_transaction+0x1a4/0xd70 fs/btrfs/transaction.c:321
       start_transaction+0x6ae/0x1620 fs/btrfs/transaction.c:705
       btrfs_rebuild_free_space_tree+0xb1/0x4e0 fs/btrfs/free-space-tree.c:1317
       btrfs_start_pre_rw_mount+0xd76/0x1180 fs/btrfs/disk-io.c:3074
       open_ctree+0x2075/0x2800 fs/btrfs/disk-io.c:3614
       btrfs_fill_super+0x19d/0x2e0 fs/btrfs/super.c:972
       btrfs_get_tree_super fs/btrfs/super.c:1897 [inline]
       btrfs_get_tree+0x107c/0x1620 fs/btrfs/super.c:2092
       vfs_get_tree+0x92/0x2b0 fs/super.c:1759
       fc_mount+0x1c/0xb0 fs/namespace.c:1289
       btrfs_get_tree_subvol fs/btrfs/super.c:2050 [inline]
       btrfs_get_tree+0x67d/0x1620 fs/btrfs/super.c:2093
       vfs_get_tree+0x92/0x2b0 fs/super.c:1759
       do_new_mount+0x24a/0xa40 fs/namespace.c:3881
       do_mount fs/namespace.c:4221 [inline]
       __do_sys_mount fs/namespace.c:4432 [inline]
       __se_sys_mount+0x317/0x410 fs/namespace.c:4409
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (btrfs_trans_num_writers){++++}-{0:0}:
       reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5383
       __lock_release kernel/locking/lockdep.c:5572 [inline]
       lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5887
       percpu_up_read include/linux/percpu-rwsem.h:100 [inline]
       __sb_end_write include/linux/fs.h:1778 [inline]
       sb_end_intwrite+0x26/0x1c0 include/linux/fs.h:1895
       __btrfs_end_transaction+0x248/0x640 fs/btrfs/transaction.c:1075
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6143
       inode_update_time fs/inode.c:2076 [inline]
       touch_atime+0x2f6/0x6d0 fs/inode.c:2149
       file_accessed include/linux/fs.h:2599 [inline]
       btrfs_file_mmap+0xbf/0x120 fs/btrfs/file.c:1938
       call_mmap include/linux/fs.h:2243 [inline]
       mmap_file mm/internal.h:167 [inline]
       __mmap_new_file_vma mm/vma.c:2353 [inline]
       __mmap_new_vma mm/vma.c:2417 [inline]
       __mmap_region mm/vma.c:2519 [inline]
       mmap_region+0x103b/0x1e50 mm/vma.c:2597
       do_mmap+0xc68/0x1100 mm/mmap.c:561
       vm_mmap_pgoff+0x31b/0x4c0 mm/util.c:579
       ksys_mmap_pgoff+0x51f/0x760 mm/mmap.c:607
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&mm->mmap_lock){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
       down_read_killable+0x50/0x350 kernel/locking/rwsem.c:1547
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:193
       get_mmap_lock_carefully mm/memory.c:6355 [inline]
       lock_mm_and_find_vma+0x2a8/0x300 mm/memory.c:6406
       do_user_addr_fault+0x331/0x1390 arch/x86/mm/fault.c:1360
       handle_page_fault arch/x86/mm/fault.c:1480 [inline]
       exc_page_fault+0x68/0x110 arch/x86/mm/fault.c:1538
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
       user_access_begin arch/x86/include/asm/uaccess.h:-1 [inline]
       filldir64+0x299/0x690 fs/readdir.c:366
       dir_emit include/linux/fs.h:3861 [inline]
       kernfs_fop_readdir+0x534/0x870 fs/kernfs/dir.c:1907
       iterate_dir+0x5ac/0x770 fs/readdir.c:108
       __do_sys_getdents64 fs/readdir.c:403 [inline]
       __se_sys_getdents64+0xe4/0x260 fs/readdir.c:389
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&root->kernfs_rwsem){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
       down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
       kernfs_add_one+0x41/0x520 fs/kernfs/dir.c:791
       kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1091
       sysfs_create_dir_ns+0x123/0x280 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x59f/0xb40 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:2616
       btrfs_quota_enable+0x278/0x1d50 fs/btrfs/qgroup.c:1030
       btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3676
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3166 [inline]
       check_prevs_add kernel/locking/lockdep.c:3285 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3909
       __lock_acquire+0xaac/0xd20 kernel/locking/lockdep.c:5235
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
       __mutex_lock_common kernel/locking/mutex.c:601 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
       btrfs_quota_enable+0x2be/0x1d50 fs/btrfs/qgroup.c:1059
       btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3676
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf6/0x210 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:
  &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 ***

5 locks held by syz.0.60/6428:
 #0: ffff888054536420 (sb_writers#20){.+.+}-{0:0}, at: mnt_want_write_file+0x60/0x200 fs/namespace.c:600
 #1: ffff888059e68bd0 (&fs_info->subvol_sem){+.+.}-{4:4}, at: btrfs_ioctl_quota_ctl+0x178/0x1c0 fs/btrfs/ioctl.c:3675
 #2: ffff888054536610 (sb_internal#3){.+.+}-{0:0}, at: btrfs_quota_enable+0x2b1/0x1d50 fs/btrfs/qgroup.c:1057
 #3: ffff888059e6a4d0 (btrfs_trans_num_writers){++++}-{0:0}, at: join_transaction+0x164/0xd70 fs/btrfs/transaction.c:320
 #4: ffff888059e6a4f8 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x164/0xd70 fs/btrfs/transaction.c:320

stack backtrace:
CPU: 0 UID: 0 PID: 6428 Comm: syz.0.60 Not tainted 6.15.0-rc6-syzkaller-00085-gc94d59a126cb #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2079
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2211
 check_prev_add kernel/locking/lockdep.c:3166 [inline]
 check_prevs_add kernel/locking/lockdep.c:3285 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3909
 __lock_acquire+0xaac/0xd20 kernel/locking/lockdep.c:5235
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
 __mutex_lock_common kernel/locking/mutex.c:601 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:746
 btrfs_quota_enable+0x2be/0x1d50 fs/btrfs/qgroup.c:1059
 btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3676
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ffbac18e969
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:00007ffbad070038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffbac3b5fa0 RCX: 00007ffbac18e969
RDX: 0000200000000580 RSI: 00000000c0109428 RDI: 0000000000000003
RBP: 00007ffbac210ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007ffbac3b5fa0 R15: 00007fff1c3f8978
 </TASK>