[v5.15] possible deadlock in quotactl_fd

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b9d57c40a767 Linux 5.15.203
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14618836580000
kernel config: https://syzkaller.appspot.com/x/.config?x=353ae28c40b35af5
dashboard link: https://syzkaller.appspot.com/bug?extid=1b1ee4d8785631fe2873
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/34313629ba4f/disk-b9d57c40.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/402f526e5a98/vmlinux-b9d57c40.xz
kernel image: https://storage.googleapis.com/syzbot-assets/45f7694e9617/bzImage-b9d57c40.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1b1ee4...@syzkaller.appspotmail.com

REISERFS (device loop2): checking transaction log (loop2)
REISERFS (device loop2): Using r5 hash to sort names
REISERFS warning (device loop2): vs-13060 reiserfs_update_sd_size: stat data of object [1 2 0x0 SD] (nlink == 1) not found (pos 2)
REISERFS (device loop2): Created .reiserfs_priv - reserved for xattr storage.
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.233/5178 is trying to acquire lock:
ffff88807494e0e0 (&type->s_umount_key#86){+.+.}-{3:3}, at: __do_sys_quotactl_fd fs/quota/quota.c:996 [inline]
ffff88807494e0e0 (&type->s_umount_key#86){+.+.}-{3:3}, at: __se_sys_quotactl_fd+0x24c/0x3b0 fs/quota/quota.c:971

but task is already holding lock:
ffff88807494e460 (sb_writers#26){.+.+}-{0:0}, at: mnt_want_write+0x3d/0x90 fs/namespace.c:386

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (sb_writers#26){.+.+}-{0:0}:
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1811 [inline]
sb_start_write+0x4f/0x1c0 include/linux/fs.h:1881
mnt_want_write_file+0x5c/0x200 fs/namespace.c:430
reiserfs_ioctl+0x10a/0x330 fs/reiserfs/ioctl.c:103
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #1 (&sbi->lock){+.+.}-{3:3}:
__mutex_lock_common+0x1e3/0x2400 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
reiserfs_write_lock+0x75/0xd0 fs/reiserfs/lock.c:27
reiserfs_put_super+0xc6/0x510 fs/reiserfs/super.c:596
generic_shutdown_super+0x130/0x300 fs/super.c:475
kill_block_super+0x7c/0xe0 fs/super.c:1427
deactivate_locked_super+0x93/0xf0 fs/super.c:335
cleanup_mnt+0x42d/0x4e0 fs/namespace.c:1148
task_work_run+0x125/0x1a0 kernel/task_work.c:188
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop+0x10f/0x130 kernel/entry/common.c:181
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #0 (&type->s_umount_key#86){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x2c42/0x7d10 kernel/locking/lockdep.c:5012
lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
down_write+0x38/0x60 kernel/locking/rwsem.c:1551
__do_sys_quotactl_fd fs/quota/quota.c:996 [inline]
__se_sys_quotactl_fd+0x24c/0x3b0 fs/quota/quota.c:971
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

Chain exists of:
&type->s_umount_key#86 --> &sbi->lock --> sb_writers#26

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(sb_writers#26);
lock(&sbi->lock);
lock(sb_writers#26);
lock(&type->s_umount_key#86);

*** DEADLOCK ***

1 lock held by syz.2.233/5178:
#0: ffff88807494e460 (sb_writers#26){.+.+}-{0:0}, at: mnt_want_write+0x3d/0x90 fs/namespace.c:386

stack backtrace:
CPU: 0 PID: 5178 Comm: syz.2.233 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
check_noncircular+0x296/0x330 kernel/locking/lockdep.c:2133
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x2c42/0x7d10 kernel/locking/lockdep.c:5012
lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
down_write+0x38/0x60 kernel/locking/rwsem.c:1551
__do_sys_quotactl_fd fs/quota/quota.c:996 [inline]
__se_sys_quotactl_fd+0x24c/0x3b0 fs/quota/quota.c:971
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f99cca6d819
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:00007f99cacc7028 EFLAGS: 00000246 ORIG_RAX: 00000000000001bb
RAX: ffffffffffffffda RBX: 00007f99ccce6fa0 RCX: 00007f99cca6d819
RDX: 0000000000000000 RSI: ffffffff80000301 RDI: 0000000000000006
RBP: 00007f99ccb03c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f99ccce7038 R14: 00007f99ccce6fa0 R15: 00007fffb198eff8
</TASK>


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: b9d57c40a767 Linux 5.15.203
git tree: linux-5.15.y

console output: https://syzkaller.appspot.com/x/log.txt?x=14a814ce580000

kernel config: https://syzkaller.appspot.com/x/.config?x=353ae28c40b35af5
dashboard link: https://syzkaller.appspot.com/bug?extid=1b1ee4d8785631fe2873
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1288a1ba580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13d5d4ce580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/34313629ba4f/disk-b9d57c40.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/402f526e5a98/vmlinux-b9d57c40.xz
kernel image: https://storage.googleapis.com/syzbot-assets/45f7694e9617/bzImage-b9d57c40.xz

mounted in repro #1: https://storage.googleapis.com/syzbot-assets/d2bd3765d132/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=10359906580000)
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/4b2019fc5e1c/mount_3.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=15d5d4ce580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1b1ee4...@syzkaller.appspotmail.com

REISERFS (device loop0): Using r5 hash to sort names
REISERFS warning (device loop0): vs-13060 reiserfs_update_sd_size: stat data of object [1 2 0x0 SD] (nlink == 1) not found (pos 2)
REISERFS (device loop0): Created .reiserfs_priv - reserved for xattr storage.

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------

syz.0.36/4408 is trying to acquire lock:
ffff88801ed1c0e0 (&type->s_umount_key#53){+.+.}-{3:3}, at: __do_sys_quotactl_fd fs/quota/quota.c:996 [inline]
ffff88801ed1c0e0 (&type->s_umount_key#53){+.+.}-{3:3}, at: __se_sys_quotactl_fd+0x24c/0x3b0 fs/quota/quota.c:971

but task is already holding lock:

ffff88801ed1c460 (sb_writers#13){.+.+}-{0:0}, at: mnt_want_write+0x3d/0x90 fs/namespace.c:386

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (sb_writers#13){.+.+}-{0:0}:

-> #0 (&type->s_umount_key#53){+.+.}-{3:3}:

check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x2c42/0x7d10 kernel/locking/lockdep.c:5012
lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
down_write+0x38/0x60 kernel/locking/rwsem.c:1551
__do_sys_quotactl_fd fs/quota/quota.c:996 [inline]
__se_sys_quotactl_fd+0x24c/0x3b0 fs/quota/quota.c:971
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

Chain exists of:

&type->s_umount_key#53 --> &sbi->lock --> sb_writers#13

Possible unsafe locking scenario:

CPU0 CPU1
---- ----

lock(sb_writers#13);
lock(&sbi->lock);
lock(sb_writers#13);
lock(&type->s_umount_key#53);

*** DEADLOCK ***

1 lock held by syz.0.36/4408:
#0: ffff88801ed1c460 (sb_writers#13){.+.+}-{0:0}, at: mnt_want_write+0x3d/0x90 fs/namespace.c:386

stack backtrace:
CPU: 0 PID: 4408 Comm: syz.0.36 Not tainted syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
check_noncircular+0x296/0x330 kernel/locking/lockdep.c:2133
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x2c42/0x7d10 kernel/locking/lockdep.c:5012
lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
down_write+0x38/0x60 kernel/locking/rwsem.c:1551
__do_sys_quotactl_fd fs/quota/quota.c:996 [inline]
__se_sys_quotactl_fd+0x24c/0x3b0 fs/quota/quota.c:971
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

RIP: 0033:0x7fda8452b819

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:00007fff4611bb88 EFLAGS: 00000246 ORIG_RAX: 00000000000001bb
RAX: ffffffffffffffda RBX: 00007fda847a4fa0 RCX: 00007fda8452b819
RDX: 0000000000000000 RSI: ffffffff80000301 RDI: 0000000000000004
RBP: 00007fda845c1c91 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 00007fda847a4fac R14: 00007fda847a4fa0 R15: 00007fda847a4fa0
</TASK>


---
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