[moderation] [fs?] possible deadlock in mnt_want_write (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9094662f6707 Merge tag 'ata-6.19-rc2' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17c70b1a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
dashboard link: https://syzkaller.appspot.com/bug?extid=746433a644b227dc2308
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/df3fce69c21a/disk-9094662f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/182b66a92309/vmlinux-9094662f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0cccba3c045d/bzImage-9094662f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+746433...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.647/8372 is trying to acquire lock:
ffff8880259d8420 (sb_writers#3){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:499

but task is already holding lock:
ffff88803403a0a8 (&ctx->uring_lock){+.+.}-{4:4}, at: __do_sys_io_uring_enter io_uring/io_uring.c:3279 [inline]
ffff88803403a0a8 (&ctx->uring_lock){+.+.}-{4:4}, at: __se_sys_io_uring_enter+0x2d5/0x2b60 io_uring/io_uring.c:3219

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&ctx->uring_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:614 [inline]
__mutex_lock+0x187/0x1350 kernel/locking/mutex.c:776
io_uring_del_tctx_node+0xf0/0x2c0 io_uring/tctx.c:179
io_uring_clean_tctx+0xd4/0x1a0 io_uring/tctx.c:195
io_uring_cancel_generic+0x6ca/0x7d0 io_uring/cancel.c:646
io_uring_task_cancel include/linux/io_uring.h:24 [inline]
begin_new_exec+0x10ed/0x2440 fs/exec.c:1131
load_elf_binary+0x9f8/0x2d70 fs/binfmt_elf.c:1010
search_binary_handler fs/exec.c:1669 [inline]
exec_binprm fs/exec.c:1701 [inline]
bprm_execve+0x92e/0x1400 fs/exec.c:1753
do_execveat_common+0x510/0x6a0 fs/exec.c:1859
do_execveat fs/exec.c:1944 [inline]
__do_sys_execveat fs/exec.c:2018 [inline]
__se_sys_execveat fs/exec.c:2012 [inline]
__x64_sys_execveat+0xc4/0xe0 fs/exec.c:2012
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&sig->cred_guard_mutex){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:614 [inline]
__mutex_lock+0x187/0x1350 kernel/locking/mutex.c:776
proc_pid_attr_write+0x547/0x630 fs/proc/base.c:2837
vfs_write+0x27e/0xb30 fs/read_write.c:684
ksys_write+0x145/0x250 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_writers#3){.+.+}-{0:0}:
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+0x107/0x340 kernel/locking/lockdep.c:5868
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
__sb_start_write include/linux/fs/super.h:19 [inline]
sb_start_write+0x4d/0x1c0 include/linux/fs/super.h:125
mnt_want_write+0x41/0x90 fs/namespace.c:499
open_last_lookups fs/namei.c:4529 [inline]
path_openat+0xadd/0x3dd0 fs/namei.c:4784
do_filp_open+0x1fa/0x410 fs/namei.c:4814
io_openat2+0x3e0/0x5c0 io_uring/openclose.c:143
__io_issue_sqe+0x181/0x4b0 io_uring/io_uring.c:1792
io_issue_sqe+0x165/0x1060 io_uring/io_uring.c:1815
io_queue_sqe io_uring/io_uring.c:2042 [inline]
io_submit_sqe io_uring/io_uring.c:2320 [inline]
io_submit_sqes+0xbf4/0x2140 io_uring/io_uring.c:2434
__do_sys_io_uring_enter io_uring/io_uring.c:3280 [inline]
__se_sys_io_uring_enter+0x2e0/0x2b60 io_uring/io_uring.c:3219
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xec/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:
sb_writers#3 --> &sig->cred_guard_mutex --> &ctx->uring_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&ctx->uring_lock);
lock(&sig->cred_guard_mutex);
lock(&ctx->uring_lock);
rlock(sb_writers#3);

*** DEADLOCK ***

1 lock held by syz.0.647/8372:
#0: ffff88803403a0a8 (&ctx->uring_lock){+.+.}-{4:4}, at: __do_sys_io_uring_enter io_uring/io_uring.c:3279 [inline]
#0: ffff88803403a0a8 (&ctx->uring_lock){+.+.}-{4:4}, at: __se_sys_io_uring_enter+0x2d5/0x2b60 io_uring/io_uring.c:3219

stack backtrace:
CPU: 0 UID: 0 PID: 8372 Comm: syz.0.647 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 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+0x107/0x340 kernel/locking/lockdep.c:5868
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
__sb_start_write include/linux/fs/super.h:19 [inline]
sb_start_write+0x4d/0x1c0 include/linux/fs/super.h:125
mnt_want_write+0x41/0x90 fs/namespace.c:499
open_last_lookups fs/namei.c:4529 [inline]
path_openat+0xadd/0x3dd0 fs/namei.c:4784
do_filp_open+0x1fa/0x410 fs/namei.c:4814
io_openat2+0x3e0/0x5c0 io_uring/openclose.c:143
__io_issue_sqe+0x181/0x4b0 io_uring/io_uring.c:1792
io_issue_sqe+0x165/0x1060 io_uring/io_uring.c:1815
io_queue_sqe io_uring/io_uring.c:2042 [inline]
io_submit_sqe io_uring/io_uring.c:2320 [inline]
io_submit_sqes+0xbf4/0x2140 io_uring/io_uring.c:2434
__do_sys_io_uring_enter io_uring/io_uring.c:3280 [inline]
__se_sys_io_uring_enter+0x2e0/0x2b60 io_uring/io_uring.c:3219
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fcffab8f749
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:00007fcffb980038 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
RAX: ffffffffffffffda RBX: 00007fcffade5fa0 RCX: 00007fcffab8f749
RDX: 0000000000000000 RSI: 0000000000003516 RDI: 0000000000000009
RBP: 00007fcffac13f91 R08: 0000000000000000 R09: 00000000fffffdcf
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fcffade6038 R14: 00007fcffade5fa0 R15: 00007fcffaf0fa28
</TASK>


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