syzbot

======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc7-syzkaller-00018-g01a412d06bc5 #0 Not tainted
------------------------------------------------------
syz.5.113/7003 is trying to acquire lock:
ffff888034529988 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}, at: btrfs_quota_enable+0x2be/0x1d50 fs/btrfs/qgroup.c:1059

but task is already holding lock:
ffff88803452a530 (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:5871
       join_transaction+0x1a4/0xd70 fs/btrfs/transaction.c:321
       start_transaction+0x6b6/0x1620 fs/btrfs/transaction.c:705
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6225
       inode_update_time fs/inode.c:2076 [inline]
       __file_update_time fs/inode.c:2305 [inline]
       file_modified_flags+0x3f1/0x560 fs/inode.c:2376
       btrfs_fallocate+0x580/0x1ba0 fs/btrfs/file.c:3073
       vfs_fallocate+0x6a0/0x830 fs/open.c:341
       ksys_fallocate fs/open.c:365 [inline]
       __do_sys_fallocate fs/open.c:370 [inline]
       __se_sys_fallocate fs/open.c:368 [inline]
       __x64_sys_fallocate+0xc0/0x110 fs/open.c:368
       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_writers){++++}-{0:0}:
       reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5388
       __lock_release kernel/locking/lockdep.c:5577 [inline]
       lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5892
       percpu_up_read include/linux/percpu-rwsem.h:112 [inline]
       __sb_end_write include/linux/fs.h:1790 [inline]
       sb_end_intwrite+0x26/0x1c0 include/linux/fs.h:1907
       __btrfs_end_transaction+0x248/0x640 fs/btrfs/transaction.c:1076
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6239
       inode_update_time fs/inode.c:2076 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2149
       file_accessed include/linux/fs.h:2652 [inline]
       btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:1988
       call_mmap include/linux/fs.h:2286 [inline]
       mmap_file mm/internal.h:167 [inline]
       __mmap_new_file_vma mm/vma.c:2405 [inline]
       __mmap_new_vma mm/vma.c:2467 [inline]
       __mmap_region mm/vma.c:2622 [inline]
       mmap_region+0x127a/0x1f30 mm/vma.c:2692
       do_mmap+0xc45/0x10d0 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+0xfa/0x3b0 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:5871
       down_read_killable+0x50/0x350 kernel/locking/rwsem.c:1547
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:421
       get_mmap_lock_carefully mm/mmap_lock.c:197 [inline]
       lock_mm_and_find_vma+0x2a8/0x300 mm/mmap_lock.c:248
       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:3921 [inline]
       kernfs_fop_readdir+0x534/0x870 fs/kernfs/dir.c:1910
       iterate_dir+0x5af/0x770 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

-> #1 (&root->kernfs_rwsem){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       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:1093
       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:2635
       btrfs_quota_enable+0x278/0x1d50 fs/btrfs/qgroup.c:1030
       btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3673
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893
       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 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       btrfs_quota_enable+0x2be/0x1d50 fs/btrfs/qgroup.c:1059
       btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3673
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893
       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:
  &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.5.113/7003:
 #0: ffff88805dda8428 (sb_writers#16){.+.+}-{0:0}, at: mnt_want_write_file+0x60/0x200 fs/namespace.c:601
 #1: ffff888034528c40 (&fs_info->subvol_sem){+.+.}-{4:4}, at: btrfs_ioctl_quota_ctl+0x178/0x1c0 fs/btrfs/ioctl.c:3672
 #2: ffff88805dda8618 (sb_internal#3){.+.+}-{0:0}, at: btrfs_quota_enable+0x2b1/0x1d50 fs/btrfs/qgroup.c:1057
 #3: ffff88803452a508 (btrfs_trans_num_writers){++++}-{0:0}, at: join_transaction+0x164/0xd70 fs/btrfs/transaction.c:320
 #4: ffff88803452a530 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x164/0xd70 fs/btrfs/transaction.c:320

stack backtrace:
CPU: 0 UID: 0 PID: 7003 Comm: syz.5.113 Not tainted 6.16.0-rc7-syzkaller-00018-g01a412d06bc5 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 __mutex_lock_common kernel/locking/mutex.c:602 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
 btrfs_quota_enable+0x2be/0x1d50 fs/btrfs/qgroup.c:1059
 btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3673
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893
 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: 0033:0x7fb80918e9a9
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:00007fb809fa1038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fb8093b5fa0 RCX: 00007fb80918e9a9
RDX: 0000200000000580 RSI: 00000000c0109428 RDI: 0000000000000003
RBP: 00007fb809210d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fb8093b5fa0 R15: 00007fff625d9e08
 </TASK>