Message-ID: <684cb50e.a00a0220.279073.0019.GAE@google.com>
Date: Fri, 13 Jun 2025 16:32:30 -0700
From: syzbot <syzbot+a16a4917cc8df9582272@...kaller.appspotmail.com>
To: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com, tj@...nel.org
Subject: [syzbot] [kernfs?] possible deadlock in mnt_want_write (6)

Hello,

syzbot found the following issue on:

HEAD commit:    475c850a7fdd Add linux-next specific files for 20250606
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17aea9d4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=28859360c84ac63d
dashboard link: https://syzkaller.appspot.com/bug?extid=a16a4917cc8df9582272
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2f1cf8485b7a/disk-475c850a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/976adb9f739e/vmlinux-475c850a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0ac20b1308b7/bzImage-475c850a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a16a4917cc8df9582272@...kaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.15.0-next-20250606-syzkaller #0 Not tainted
------------------------------------------------------
syz.1.1351/13335 is trying to acquire lock:
ffff888035b3c428 (sb_writers#5){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:557

but task is already holding lock:
ffff888059674100 (&ovl_i_mutex_dir_key[depth]#2){++++}-{4:4}, at: inode_lock include/linux/fs.h:867 [inline]
ffff888059674100 (&ovl_i_mutex_dir_key[depth]#2){++++}-{4:4}, at: open_last_lookups fs/namei.c:3804 [inline]
ffff888059674100 (&ovl_i_mutex_dir_key[depth]#2){++++}-{4:4}, at: path_openat+0x8da/0x3830 fs/namei.c:4043

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&ovl_i_mutex_dir_key[depth]#2){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       down_read+0x46/0x2e0 kernel/locking/rwsem.c:1524
       inode_lock_shared include/linux/fs.h:882 [inline]
       lookup_slow+0x46/0x70 fs/namei.c:1833
       walk_component+0x2d2/0x400 fs/namei.c:2138
       lookup_last fs/namei.c:2639 [inline]
       path_lookupat+0x163/0x430 fs/namei.c:2663
       filename_lookup+0x212/0x570 fs/namei.c:2692
       kern_path+0x35/0x50 fs/namei.c:2825
       lookup_bdev+0xc0/0x280 block/bdev.c:1205
       resume_store+0x169/0x460 kernel/power/hibernate.c:1272
       kernfs_fop_write_iter+0x378/0x4f0 fs/kernfs/file.c:334
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x54b/0xa90 fs/read_write.c:686
       ksys_write+0x145/0x250 fs/read_write.c:738
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&of->mutex){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       kernfs_fop_write_iter+0x1e0/0x4f0 fs/kernfs/file.c:325
       iter_file_splice_write+0x937/0x1000 fs/splice.c:738
       do_splice_from fs/splice.c:935 [inline]
       do_splice+0xc79/0x1660 fs/splice.c:1348
       __do_splice fs/splice.c:1430 [inline]
       __do_sys_splice fs/splice.c:1633 [inline]
       __se_sys_splice+0x2e1/0x460 fs/splice.c:1615
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&pipe->mutex){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       iter_file_splice_write+0x1e6/0x1000 fs/splice.c:683
       do_splice_from fs/splice.c:935 [inline]
       do_splice+0xc79/0x1660 fs/splice.c:1348
       __do_splice fs/splice.c:1430 [inline]
       __do_sys_splice fs/splice.c:1633 [inline]
       __se_sys_splice+0x2e1/0x460 fs/splice.c:1615
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_writers#5){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       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.h:1793 [inline]
       sb_start_write+0x4d/0x1c0 include/linux/fs.h:1929
       mnt_want_write+0x41/0x90 fs/namespace.c:557
       ovl_create_object+0xfc/0x310 fs/overlayfs/dir.c:628
       lookup_open fs/namei.c:3708 [inline]
       open_last_lookups fs/namei.c:3807 [inline]
       path_openat+0x14f1/0x3830 fs/namei.c:4043
       do_filp_open+0x1fa/0x410 fs/namei.c:4073
       do_sys_openat2+0x121/0x1c0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_creat fs/open.c:1530 [inline]
       __se_sys_creat fs/open.c:1524 [inline]
       __x64_sys_creat+0x8f/0xc0 fs/open.c:1524
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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#5 --> &of->mutex --> &ovl_i_mutex_dir_key[depth]#2

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&ovl_i_mutex_dir_key[depth]#2);
                               lock(&of->mutex);
                               lock(&ovl_i_mutex_dir_key[depth]#2);
  rlock(sb_writers#5);

 *** DEADLOCK ***

2 locks held by syz.1.1351/13335:
 #0: ffff888027172428
 (sb_writers#27){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:557
 #1: 
ffff888059674100
 (&ovl_i_mutex_dir_key[depth]
#2){++++}-{4:4}, at: inode_lock include/linux/fs.h:867 [inline]
#2){++++}-{4:4}, at: open_last_lookups fs/namei.c:3804 [inline]
#2){++++}-{4:4}, at: path_openat+0x8da/0x3830 fs/namei.c:4043

stack backtrace:
CPU: 1 UID: 0 PID: 13335 Comm: syz.1.1351 Not tainted 6.15.0-next-20250606-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 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.h:1793 [inline]
 sb_start_write+0x4d/0x1c0 include/linux/fs.h:1929
 mnt_want_write+0x41/0x90 fs/namespace.c:557
 ovl_create_object+0xfc/0x310 fs/overlayfs/dir.c:628
 lookup_open fs/namei.c:3708 [inline]
 open_last_lookups fs/namei.c:3807 [inline]
 path_openat+0x14f1/0x3830 fs/namei.c:4043
 do_filp_open+0x1fa/0x410 fs/namei.c:4073
 do_sys_openat2+0x121/0x1c0 fs/open.c:1437
 do_sys_open fs/open.c:1452 [inline]
 __do_sys_creat fs/open.c:1530 [inline]
 __se_sys_creat fs/open.c:1524 [inline]
 __x64_sys_creat+0x8f/0xc0 fs/open.c:1524
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f14eef8e929
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:00007f14ecdf6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
RAX: ffffffffffffffda RBX: 00007f14ef1b5fa0 RCX: 00007f14eef8e929
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00002000000002c0
RBP: 00007f14ef010b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f14ef1b5fa0 R15: 00007fff1db0f028
 </TASK>


---
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