[v5.15] possible deadlock in mnt_want_write (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6e2fd6534337 Linux 5.15.213
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14004bb9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f161cbc9aef65db0
dashboard link: https://syzkaller.appspot.com/bug?extid=cea9a42a76b62d4d03c5
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d7b46606b13d/disk-6e2fd653.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/da120fdeb081/vmlinux-6e2fd653.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3c2643457e3f/bzImage-6e2fd653.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cea9a4...@syzkaller.appspotmail.com

Mass Storage Function, version: 2009/09/11
LUN: removable file: (no medium)
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.6.239/5141 is trying to acquire lock:
ffff888078372460 (sb_writers#3){.+.+}-{0:0}, at: mnt_want_write+0x3d/0x90 fs/namespace.c:386

but task is already holding lock:
ffff888078f66128 (&common->filesem){++++}-{3:3}, at: fsg_store_file+0x174/0x530 drivers/usb/gadget/function/storage_common.c:451

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&common->filesem){++++}-{3:3}:
down_read+0x44/0x2e0 kernel/locking/rwsem.c:1498
fsg_show_file+0x29/0x130 drivers/usb/gadget/function/storage_common.c:338
fill_read_buffer fs/configfs/file.c:68 [inline]
configfs_read_iter+0x296/0x560 fs/configfs/file.c:88
__kernel_read+0x51d/0x980 fs/read_write.c:443
integrity_kernel_read+0x86/0xd0 security/integrity/iint.c:228
ima_calc_file_hash_tfm security/integrity/ima/ima_crypto.c:485 [inline]
ima_calc_file_shash security/integrity/ima/ima_crypto.c:516 [inline]
ima_calc_file_hash+0x946/0x1940 security/integrity/ima/ima_crypto.c:573
ima_collect_measurement+0x335/0x7e0 security/integrity/ima/ima_api.c:255
process_measurement+0x1185/0x1c20 security/integrity/ima/ima_main.c:351
ima_file_check+0xc7/0x110 security/integrity/ima/ima_main.c:533
do_open fs/namei.c:3618 [inline]
path_openat+0x27cf/0x2fb0 fs/namei.c:3750
do_filp_open+0x1df/0x400 fs/namei.c:3777
do_sys_openat2+0x14b/0x500 fs/open.c:1255
do_sys_open fs/open.c:1271 [inline]
__do_sys_openat fs/open.c:1287 [inline]
__se_sys_openat fs/open.c:1282 [inline]
__x64_sys_openat+0x135/0x160 fs/open.c:1282
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

-> #2 (&p->frag_sem){.+.+}-{3:3}:
down_read+0x44/0x2e0 kernel/locking/rwsem.c:1498
__configfs_open_file+0xd5/0x7d0 fs/configfs/file.c:304
do_dentry_open+0x7f7/0xf90 fs/open.c:826
vfs_open fs/open.c:958 [inline]
dentry_open+0xc6/0x120 fs/open.c:974
ima_calc_file_hash+0x18c/0x1940 security/integrity/ima/ima_crypto.c:558
ima_collect_measurement+0x335/0x7e0 security/integrity/ima/ima_api.c:255
process_measurement+0x1185/0x1c20 security/integrity/ima/ima_main.c:351
ima_file_check+0xc7/0x110 security/integrity/ima/ima_main.c:533
do_open fs/namei.c:3618 [inline]
path_openat+0x27cf/0x2fb0 fs/namei.c:3750
do_filp_open+0x1df/0x400 fs/namei.c:3777
do_sys_openat2+0x14b/0x500 fs/open.c:1255
do_sys_open fs/open.c:1271 [inline]
__do_sys_openat fs/open.c:1287 [inline]
__se_sys_openat fs/open.c:1282 [inline]
__x64_sys_openat+0x135/0x160 fs/open.c:1282
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 (&iint_mutex_key[depth]){+.+.}-{3:3}:
__mutex_lock_common+0x1e5/0x2400 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
process_measurement+0x724/0x1c20 security/integrity/ima/ima_main.c:261
ima_file_check+0xc7/0x110 security/integrity/ima/ima_main.c:533
do_open fs/namei.c:3618 [inline]
path_openat+0x27cf/0x2fb0 fs/namei.c:3750
do_filp_open+0x1df/0x400 fs/namei.c:3777
do_sys_openat2+0x14b/0x500 fs/open.c:1255
do_sys_open fs/open.c:1271 [inline]
__do_sys_openat fs/open.c:1287 [inline]
__se_sys_openat fs/open.c:1282 [inline]
__x64_sys_openat+0x135/0x160 fs/open.c:1282
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

-> #0 (sb_writers#3){.+.+}-{0:0}:
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+0x2c66/0x7b50 kernel/locking/lockdep.c:5012
lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
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+0x3d/0x90 fs/namespace.c:386
open_last_lookups fs/namei.c:3529 [inline]
path_openat+0x795/0x2fb0 fs/namei.c:3747
do_filp_open+0x1df/0x400 fs/namei.c:3777
file_open_name fs/open.c:1200 [inline]
filp_open+0x17c/0x1e0 fs/open.c:1220
fsg_lun_open+0x63/0xee0 drivers/usb/gadget/function/storage_common.c:193
fsg_store_file+0x1a5/0x530 drivers/usb/gadget/function/storage_common.c:454
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x30b/0x400 fs/configfs/file.c:229
call_write_iter include/linux/fs.h:2173 [inline]
new_sync_write fs/read_write.c:507 [inline]
vfs_write+0x748/0xd70 fs/read_write.c:594
ksys_write+0x153/0x260 fs/read_write.c:647
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:
sb_writers#3 --> &p->frag_sem --> &common->filesem

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&common->filesem);
lock(&p->frag_sem);
lock(&common->filesem);
lock(sb_writers#3);

*** DEADLOCK ***

5 locks held by syz.6.239/5141:
#0: ffff888078e5d770 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2bf/0x370 fs/file.c:1056
#1: ffff888146a10460 (sb_writers#31){.+.+}-{0:0}, at: vfs_write+0x296/0xd70 fs/read_write.c:590
#2: ffff8880621a5288 (&buffer->mutex){+.+.}-{3:3}, at: configfs_write_iter+0x7d/0x400 fs/configfs/file.c:226
#3: ffff888148c42778 (&p->frag_sem){.+.+}-{3:3}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
#3: ffff888148c42778 (&p->frag_sem){.+.+}-{3:3}, at: configfs_write_iter+0x20e/0x400 fs/configfs/file.c:229
#4: ffff888078f66128 (&common->filesem){++++}-{3:3}, at: fsg_store_file+0x174/0x530 drivers/usb/gadget/function/storage_common.c:451

stack backtrace:
CPU: 0 PID: 5141 Comm: syz.6.239 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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+0x2c66/0x7b50 kernel/locking/lockdep.c:5012
lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
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+0x3d/0x90 fs/namespace.c:386
open_last_lookups fs/namei.c:3529 [inline]
path_openat+0x795/0x2fb0 fs/namei.c:3747
do_filp_open+0x1df/0x400 fs/namei.c:3777
file_open_name fs/open.c:1200 [inline]
filp_open+0x17c/0x1e0 fs/open.c:1220
fsg_lun_open+0x63/0xee0 drivers/usb/gadget/function/storage_common.c:193
fsg_store_file+0x1a5/0x530 drivers/usb/gadget/function/storage_common.c:454
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x30b/0x400 fs/configfs/file.c:229
call_write_iter include/linux/fs.h:2173 [inline]
new_sync_write fs/read_write.c:507 [inline]
vfs_write+0x748/0xd70 fs/read_write.c:594
ksys_write+0x153/0x260 fs/read_write.c:647
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: 0033:0x7fe465f79019
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:00007fe4641d1028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fe466200fa0 RCX: 00007fe465f79019
RDX: 0000000000000001 RSI: 0000200000000f00 RDI: 0000000000000003
RBP: 00007fe46601000c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe466201038 R14: 00007fe466200fa0 R15: 00007fff090a3748
</TASK>
mass_storage.usb0/lun.0: unable to open backing file: f


---
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 syzk...@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