[syzbot] [kernfs?] possible deadlock in kernfs_fop_write_iter (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 87320be9f0d2 Merge tag 'net-7.2-rc2' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=173580d6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d69870d5e052935f
dashboard link: https://syzkaller.appspot.com/bug?extid=c236d648c8a2fb8dd178
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b66380bc19e0/disk-87320be9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7c039967f4a2/vmlinux-87320be9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/71de88cff101/bzImage-87320be9.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c236d6...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.5.9374/32409 is trying to acquire lock:
ffff88807b14f080 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:336

but task is already holding lock:
ffff8880566b1060 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
ffff8880566b1060 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock+0x69/0x80 fs/pipe.c:88

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&pipe->mutex){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
pipe_lock fs/pipe.c:91 [inline]
pipe_lock+0x69/0x80 fs/pipe.c:88
iter_file_splice_write+0x1fd/0x10b0 fs/splice.c:682
backing_file_splice_write+0x27b/0x820 fs/backing-file.c:318
ovl_splice_write+0x328/0x610 fs/overlayfs/file.c:433
do_splice_from fs/splice.c:936 [inline]
do_splice+0x109c/0x1f90 fs/splice.c:1349
__do_splice+0x33b/0x370 fs/splice.c:1431
__do_sys_splice fs/splice.c:1634 [inline]
__se_sys_splice fs/splice.c:1616 [inline]
__x64_sys_splice+0x187/0x250 fs/splice.c:1616
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (sb_writers#6){.+.+}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
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 include/linux/fs/super.h:125 [inline]
mnt_want_write+0x6f/0x410 fs/namespace.c:494
ovl_create_object+0x12b/0x3b0 fs/overlayfs/dir.c:706
lookup_open fs/namei.c:4508 [inline]
open_last_lookups fs/namei.c:4608 [inline]
path_openat+0x341f/0x4280 fs/namei.c:4856
do_file_open+0x20e/0x430 fs/namei.c:4888
do_sys_openat2+0x10f/0x1e0 fs/open.c:1368
do_sys_open fs/open.c:1374 [inline]
__do_sys_open fs/open.c:1382 [inline]
__se_sys_open fs/open.c:1378 [inline]
__x64_sys_open+0xfe/0x1d0 fs/open.c:1378
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
down_read+0x99/0x4c0 kernel/locking/rwsem.c:1574
inode_lock_shared include/linux/fs.h:1039 [inline]
lookup_slow+0x42/0x70 fs/namei.c:1935
walk_component fs/namei.c:2282 [inline]
lookup_last fs/namei.c:2789 [inline]
path_lookupat+0x5e8/0xc40 fs/namei.c:2813
filename_lookup+0x202/0x590 fs/namei.c:2842
kern_path+0x37/0x50 fs/namei.c:3036
lookup_bdev+0xd8/0x280 block/bdev.c:1208
resume_store+0x1d6/0x460 kernel/power/hibernate.c:1278
kobj_attr_store+0x58/0x80 lib/kobject.c:840
sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&of->mutex){+.+.}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:336
iter_file_splice_write+0x830/0x10b0 fs/splice.c:736
do_splice_from fs/splice.c:936 [inline]
do_splice+0x109c/0x1f90 fs/splice.c:1349
__do_splice+0x33b/0x370 fs/splice.c:1431
__do_sys_splice fs/splice.c:1634 [inline]
__se_sys_splice fs/splice.c:1616 [inline]
__x64_sys_splice+0x187/0x250 fs/splice.c:1616
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 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:
&of->mutex --> sb_writers#6 --> &pipe->mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&pipe->mutex);
lock(sb_writers#6);
lock(&pipe->mutex);
lock(&of->mutex);

*** DEADLOCK ***

2 locks held by syz.5.9374/32409:
#0: ffff888035990450 (sb_writers#8){.+.+}-{0:0}, at: __do_splice+0x33b/0x370 fs/splice.c:1431
#1: ffff8880566b1060 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
#1: ffff8880566b1060 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock+0x69/0x80 fs/pipe.c:88

stack backtrace:
CPU: 1 UID: 0 PID: 32409 Comm: syz.5.9374 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/10/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:336
iter_file_splice_write+0x830/0x10b0 fs/splice.c:736
do_splice_from fs/splice.c:936 [inline]
do_splice+0x109c/0x1f90 fs/splice.c:1349
__do_splice+0x33b/0x370 fs/splice.c:1431
__do_sys_splice fs/splice.c:1634 [inline]
__se_sys_splice fs/splice.c:1616 [inline]
__x64_sys_splice+0x187/0x250 fs/splice.c:1616
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa20679de59
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:00007fa2049f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007fa206a26180 RCX: 00007fa20679de59
RDX: 0000000000000009 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007fa206833e6f R08: 000000000000bfd1 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa206a26218 R14: 00007fa206a26180 R15: 00007ffeeeb4de38
</TASK>


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