[syzbot] [btrfs?] possible deadlock in btrfs_quota_enable (2)

syzbot
2025-05-10T20:51:25Z

Hello,

syzbot found the following issue on:

HEAD commit: 0d8d44db295c Merge tag 'for-6.15-rc5-tag' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=135ed39b980000
kernel config: https://syzkaller.appspot.com/x/.config?x=b9683d529ec1b880
dashboard link: https://syzkaller.appspot.com/bug?extid=3a88c590edd72179657c
compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3248bbf33c7c/disk-0d8d44db.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7a1ed3b1be50/vmlinux-0d8d44db.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e6ac2567359a/bzImage-0d8d44db.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3a88c590edd72179657c@syzkaller.appspotmail.com

BTRFS info (device loop4): clearing compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)
======================================================
WARNING: possible circular locking dependency detected
6.15.0-rc5-syzkaller-00032-g0d8d44db295c #0 Not tainted
------------------------------------------------------
syz.4.219/7436 is trying to acquire lock:
ffff88806ce71918 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}, at: btrfs_quota_enable+0x2be/0x1d50 fs/btrfs/qgroup.c:1059

but task is already holding lock:
ffff88806ce724f8 (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:

-> #5 (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_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6129
inode_update_time fs/inode.c:2076 [inline]
touch_atime+0x2f6/0x6d0 fs/inode.c:2149
file_accessed include/linux/fs.h:2599 [inline]
filemap_read+0x1024/0x11d0 mm/filemap.c:2774
__kernel_read+0x469/0x8c0 fs/read_write.c:528
integrity_kernel_read+0x89/0xd0 security/integrity/iint.c:28
ima_calc_file_hash_tfm security/integrity/ima/ima_crypto.c:480 [inline]
ima_calc_file_shash security/integrity/ima/ima_crypto.c:511 [inline]
ima_calc_file_hash+0x152c/0x18d0 security/integrity/ima/ima_crypto.c:568
ima_collect_measurement+0x42e/0x8e0 security/integrity/ima/ima_api.c:293
process_measurement+0x1121/0x1a40 security/integrity/ima/ima_main.c:385
ima_file_check+0xd7/0x120 security/integrity/ima/ima_main.c:613
security_file_post_open+0xbb/0x290 security/security.c:3130
do_open fs/namei.c:3882 [inline]
path_openat+0x2f26/0x3830 fs/namei.c:4039
do_filp_open+0x1fa/0x410 fs/namei.c:4066
do_sys_openat2+0x121/0x1c0 fs/open.c:1429
do_sys_open fs/open.c:1444 [inline]
__do_sys_openat fs/open.c:1460 [inline]
__se_sys_openat fs/open.c:1455 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1455
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

-> #4 (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]
__file_update_time fs/inode.c:2305 [inline]
file_update_time+0x344/0x490 fs/inode.c:2335
btrfs_page_mkwrite+0x634/0x16a0 fs/btrfs/file.c:1814
do_page_mkwrite+0x14a/0x310 mm/memory.c:3287
wp_page_shared mm/memory.c:3688 [inline]
do_wp_page+0x2626/0x5760 mm/memory.c:3907
handle_pte_fault mm/memory.c:6013 [inline]
__handle_mm_fault+0x1028/0x5380 mm/memory.c:6140
handle_mm_fault+0x2d5/0x7f0 mm/memory.c:6309
do_user_addr_fault+0xa81/0x1390 arch/x86/mm/fault.c:1337
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

-> #3 (sb_pagefaults#2){.+.+}-{0:0}:
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5866
percpu_down_read include/linux/percpu-rwsem.h:52 [inline]
__sb_start_write include/linux/fs.h:1783 [inline]
sb_start_pagefault include/linux/fs.h:1948 [inline]
btrfs_page_mkwrite+0x3b2/0x16a0 fs/btrfs/file.c:1798
do_page_mkwrite+0x14a/0x310 mm/memory.c:3287
do_shared_fault mm/memory.c:5594 [inline]
do_fault mm/memory.c:5656 [inline]
do_pte_missing mm/memory.c:4160 [inline]
handle_pte_fault mm/memory.c:5997 [inline]
__handle_mm_fault+0x18d2/0x5380 mm/memory.c:6140
handle_mm_fault+0x2d5/0x7f0 mm/memory.c:6309
do_user_addr_fault+0x764/0x1390 arch/x86/mm/fault.c:1388
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

-> #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
filldir64+0x2b3/0x690 fs/readdir.c:371
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.4.219/7436:
#0: ffff8880259ac420 (sb_writers#17){.+.+}-{0:0}, at: mnt_want_write_file+0x60/0x200 fs/namespace.c:600
#1: ffff88806ce70bd0 (&fs_info->subvol_sem){+.+.}-{4:4}, at: btrfs_ioctl_quota_ctl+0x178/0x1c0 fs/btrfs/ioctl.c:3675
#2: ffff8880259ac610 (sb_internal#3){.+.+}-{0:0}, at: btrfs_quota_enable+0x2b1/0x1d50 fs/btrfs/qgroup.c:1057
#3: ffff88806ce724d0 (btrfs_trans_num_writers){++++}-{0:0}, at: join_transaction+0x164/0xd70 fs/btrfs/transaction.c:320
#4: ffff88806ce724f8 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x164/0xd70 fs/btrfs/transaction.c:320

stack backtrace:
CPU: 1 UID: 0 PID: 7436 Comm: syz.4.219 Not tainted 6.15.0-rc5-syzkaller-00032-g0d8d44db295c #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/29/2025
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: 0033:0x7f7c0cf8e969
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:00007f7c0adf6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f7c0d1b5fa0 RCX: 00007f7c0cf8e969
RDX: 0000200000000580 RSI: 00000000c0109428 RDI: 0000000000000003
RBP: 00007f7c0d010ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f7c0d1b5fa0 R15: 00007ffe0a7382c8
</TASK>

---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup