From: syzbot <syzbot+1a44c3c7940ab3688125@syzkaller.appspotmail.com>
To: clm@fb.com, dsterba@suse.com, josef@toxicpanda.com,
linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
syzkaller-bugs@googlegroups.com
Subject: [syzbot] [btrfs?] possible deadlock in btrfs_create_qgroup
Date: Thu, 01 Jan 2026 06:50:21 -0800 [thread overview]
Message-ID: <695689ad.050a0220.a1b6.0340.GAE@google.com> (raw)
Hello,
syzbot found the following issue on:
HEAD commit: cc3aa43b44bd Add linux-next specific files for 20251219
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15d58bda580000
kernel config: https://syzkaller.appspot.com/x/.config?x=da1bc82c6189c463
dashboard link: https://syzkaller.appspot.com/bug?extid=1a44c3c7940ab3688125
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/30bf539e6f28/disk-cc3aa43b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0e2f8b08e342/vmlinux-cc3aa43b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ec7ee6ece11f/bzImage-cc3aa43b.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1a44c3c7940ab3688125@syzkaller.appspotmail.com
BTRFS info (device loop0): max_inline set to 4096
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.0.2512/16697 is trying to acquire lock:
ffff88802f119990 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}, at: btrfs_create_qgroup+0x55/0x520 fs/btrfs/qgroup.c:1683
but task is already holding lock:
ffff88802f118d30 (&fs_info->reloc_mutex){+.+.}-{4:4}, at: btrfs_commit_transaction+0xf6b/0x3bd0 fs/btrfs/transaction.c:2424
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #5 (&fs_info->reloc_mutex){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:614 [inline]
__mutex_lock+0x187/0x1350 kernel/locking/mutex.c:776
btrfs_record_root_in_trans+0x14f/0x180 fs/btrfs/transaction.c:505
start_transaction+0x3a7/0x15f0 fs/btrfs/transaction.c:782
btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6406
inode_update_time fs/inode.c:2167 [inline]
file_update_time_flags+0x387/0x4e0 fs/inode.c:2395
__generic_remap_file_range_prep+0xb11/0xbe0 fs/remap_range.c:362
generic_remap_file_range_prep+0x3e/0x60 fs/remap_range.c:371
btrfs_remap_file_range_prep fs/btrfs/reflink.c:850 [inline]
btrfs_remap_file_range+0x645/0x1320 fs/btrfs/reflink.c:886
vfs_clone_file_range+0x42c/0x7a0 fs/remap_range.c:403
ioctl_file_clone fs/ioctl.c:239 [inline]
ioctl_file_clone_range fs/ioctl.c:257 [inline]
do_vfs_ioctl+0xd2b/0x1430 fs/ioctl.c:544
__do_sys_ioctl fs/ioctl.c:595 [inline]
__se_sys_ioctl+0x82/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #4 (btrfs_trans_num_extwriters){++++}-{0:0}:
join_transaction+0x1a4/0xd60 fs/btrfs/transaction.c:323
start_transaction+0x6ba/0x15f0 fs/btrfs/transaction.c:708
btrfs_rebuild_free_space_tree+0xad/0x6d0 fs/btrfs/free-space-tree.c:1330
btrfs_start_pre_rw_mount+0x1299/0x1c30 fs/btrfs/disk-io.c:3018
open_ctree+0x2b28/0x3d90 fs/btrfs/disk-io.c:3566
btrfs_fill_super fs/btrfs/super.c:981 [inline]
btrfs_get_tree_super fs/btrfs/super.c:1944 [inline]
btrfs_get_tree_subvol fs/btrfs/super.c:2087 [inline]
btrfs_get_tree+0x1061/0x1930 fs/btrfs/super.c:2121
vfs_get_tree+0x92/0x2a0 fs/super.c:1751
fc_mount fs/namespace.c:1199 [inline]
do_new_mount_fc fs/namespace.c:3636 [inline]
do_new_mount+0x302/0xa10 fs/namespace.c:3712
do_mount fs/namespace.c:4035 [inline]
__do_sys_mount fs/namespace.c:4224 [inline]
__se_sys_mount+0x313/0x410 fs/namespace.c:4201
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #3 (btrfs_trans_num_writers){++++}-{0:0}:
__lock_release kernel/locking/lockdep.c:5574 [inline]
lock_release+0x1ab/0x3b0 kernel/locking/lockdep.c:5889
percpu_up_read include/linux/percpu-rwsem.h:112 [inline]
__sb_end_write include/linux/fs/super.h:14 [inline]
sb_end_intwrite+0x26/0x1c0 include/linux/fs/super.h:101
__btrfs_end_transaction+0x248/0x640 fs/btrfs/transaction.c:1084
btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6420
inode_update_time fs/inode.c:2167 [inline]
touch_atime+0x2f9/0x6d0 fs/inode.c:2240
file_accessed include/linux/fs.h:2255 [inline]
btrfs_file_mmap_prepare+0x176/0x1f0 fs/btrfs/file.c:2050
vfs_mmap_prepare include/linux/fs.h:2059 [inline]
call_mmap_prepare mm/vma.c:2596 [inline]
__mmap_region mm/vma.c:2692 [inline]
mmap_region+0xb2b/0x1d10 mm/vma.c:2786
do_mmap+0xc45/0x10d0 mm/mmap.c:558
vm_mmap_pgoff+0x2a6/0x4d0 mm/util.c:581
ksys_mmap_pgoff+0x51f/0x760 mm/mmap.c:604
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #2 (&mm->mmap_lock){++++}-{4:4}:
down_read_killable+0x50/0x350 kernel/locking/rwsem.c:1560
mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:400
get_mmap_lock_carefully mm/mmap_lock.c:399 [inline]
lock_mm_and_find_vma+0x2a8/0x300 mm/mmap_lock.c:450
do_user_addr_fault+0x331/0x1380 arch/x86/mm/fault.c:1359
handle_page_fault arch/x86/mm/fault.c:1476 [inline]
exc_page_fault+0x82/0x100 arch/x86/mm/fault.c:1532
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
filldir+0x2b6/0x6c0 fs/readdir.c:295
dir_emit include/linux/fs.h:3526 [inline]
kernfs_fop_readdir+0x537/0x870 fs/kernfs/dir.c:1913
iterate_dir+0x399/0x570 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/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #1 (&root->kernfs_rwsem){++++}-{4:4}:
down_write+0x96/0x1f0 kernel/locking/rwsem.c:1590
kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:794
kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1096
sysfs_create_dir_ns+0x123/0x280 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x6ab/0xcc0 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:2643
btrfs_quota_enable+0x25d/0x2920 fs/btrfs/qgroup.c:1034
btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3613
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:63 [inline]
do_syscall_64+0xfa/0xf80 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:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
__mutex_lock_common kernel/locking/mutex.c:614 [inline]
__mutex_lock+0x187/0x1350 kernel/locking/mutex.c:776
btrfs_create_qgroup+0x55/0x520 fs/btrfs/qgroup.c:1683
create_pending_snapshot+0x86c/0x3270 fs/btrfs/transaction.c:1749
create_pending_snapshots+0x17c/0x1c0 fs/btrfs/transaction.c:1941
btrfs_commit_transaction+0xf78/0x3bd0 fs/btrfs/transaction.c:2431
create_snapshot fs/btrfs/ioctl.c:779 [inline]
btrfs_mksubvol+0xc75/0x12d0 fs/btrfs/ioctl.c:926
btrfs_mksnapshot+0xab/0xf0 fs/btrfs/ioctl.c:968
__btrfs_ioctl_snap_create+0x520/0x740 fs/btrfs/ioctl.c:1232
btrfs_ioctl_snap_create_v2+0x1f8/0x3b0 fs/btrfs/ioctl.c:1312
btrfs_ioctl+0xa62/0xd00 fs/btrfs/ioctl.c:-1
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:63 [inline]
do_syscall_64+0xfa/0xf80 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_extwriters --> &fs_info->reloc_mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&fs_info->reloc_mutex);
lock(btrfs_trans_num_extwriters);
lock(&fs_info->reloc_mutex);
lock(&fs_info->qgroup_ioctl_lock);
*** DEADLOCK ***
8 locks held by syz.0.2512/16697:
#0: ffff888054516420 (sb_writers#18){.+.+}-{0:0}, at: mnt_want_write_file+0x60/0x200 fs/namespace.c:543
#1: ffff8880442e9ed0 (&type->i_mutex_dir_key#11/1){+.+.}-{4:4}, at: __start_dirop fs/namei.c:2859 [inline]
#1: ffff8880442e9ed0 (&type->i_mutex_dir_key#11/1){+.+.}-{4:4}, at: start_creating_killable+0xc1/0x120 fs/namei.c:3387
#2: ffff88802f118c60 (&fs_info->subvol_sem){++++}-{4:4}, at: btrfs_mksubvol+0x4ce/0x12d0 fs/btrfs/ioctl.c:920
#3: ffff888054516610 (sb_internal#4){.+.+}-{0:0}, at: create_snapshot fs/btrfs/ioctl.c:764 [inline]
#3: ffff888054516610 (sb_internal#4){.+.+}-{0:0}, at: btrfs_mksubvol+0xaf2/0x12d0 fs/btrfs/ioctl.c:926
#4: ffff88802f11a5f0 (btrfs_trans_completed){++++}-{0:0}, at: btrfs_commit_transaction+0x178/0x3bd0 fs/btrfs/transaction.c:2207
#5: ffff88802f11a5c8 (btrfs_trans_super_committed){.+.+}-{0:0}, at: btrfs_commit_transaction+0x178/0x3bd0 fs/btrfs/transaction.c:2207
#6: ffff88802f11a5a0 (btrfs_trans_unblocked){.+.+}-{0:0}, at: btrfs_commit_transaction+0x178/0x3bd0 fs/btrfs/transaction.c:2207
#7: ffff88802f118d30 (&fs_info->reloc_mutex){+.+.}-{4:4}, at: btrfs_commit_transaction+0xf6b/0x3bd0 fs/btrfs/transaction.c:2424
stack backtrace:
CPU: 1 UID: 0 PID: 16697 Comm: syz.0.2512 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2043
check_noncircular+0x12e/0x150 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 kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
__mutex_lock_common kernel/locking/mutex.c:614 [inline]
__mutex_lock+0x187/0x1350 kernel/locking/mutex.c:776
btrfs_create_qgroup+0x55/0x520 fs/btrfs/qgroup.c:1683
create_pending_snapshot+0x86c/0x3270 fs/btrfs/transaction.c:1749
create_pending_snapshots+0x17c/0x1c0 fs/btrfs/transaction.c:1941
btrfs_commit_transaction+0xf78/0x3bd0 fs/btrfs/transaction.c:2431
create_snapshot fs/btrfs/ioctl.c:779 [inline]
btrfs_mksubvol+0xc75/0x12d0 fs/btrfs/ioctl.c:926
btrfs_mksnapshot+0xab/0xf0 fs/btrfs/ioctl.c:968
__btrfs_ioctl_snap_create+0x520/0x740 fs/btrfs/ioctl.c:1232
btrfs_ioctl_snap_create_v2+0x1f8/0x3b0 fs/btrfs/ioctl.c:1312
btrfs_ioctl+0xa62/0xd00 fs/btrfs/ioctl.c:-1
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:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f732378f749
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:00007f73245df038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f73239e5fa0 RCX: 00007f732378f749
RDX: 0000200000002480 RSI: 0000000050009417 RDI: 0000000000000004
RBP: 00007f7323813f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f73239e6038 R14: 00007f73239e5fa0 R15: 00007ffdae0e36b8
</TASK>
BTRFS info (device loop0): last unmount of filesystem ed167579-eb65-4e76-9a50-61ac97e9b59d
---
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.
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If the report is already addressed, let syzbot know by replying with:
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If you want to overwrite report's subsystems, reply with:
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If the report is a duplicate of another one, reply with:
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If you want to undo deduplication, reply with:
#syz undup
reply other threads:[~2026-01-01 14:50 UTC|newest]
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