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Date: Sat, 27 Apr 2024 04:09:21 -0700
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Subject: [syzbot] [kernfs?] possible deadlock in kernfs_seq_start
From: syzbot <syzbot+4c493dcd5a68168a94b2@syzkaller.appspotmail.com>
To: gregkh@linuxfoundation.org, linux-fsdevel@vger.kernel.org, 
	linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, tj@kernel.org
Content-Type: text/plain; charset="UTF-8"

Hello,

syzbot found the following issue on:

HEAD commit:    71b1543c83d6 Merge tag '6.9-rc5-ksmbd-fixes' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=132f3973180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5a05c230e142f2bc
dashboard link: https://syzkaller.appspot.com/bug?extid=4c493dcd5a68168a94b2
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c2ffdc70f4f4/disk-71b1543c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3f55cd9df875/vmlinux-71b1543c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c9547057857d/bzImage-71b1543c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4c493dcd5a68168a94b2@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.9.0-rc5-syzkaller-00031-g71b1543c83d6 #0 Not tainted
------------------------------------------------------
syz-executor.1/17062 is trying to acquire lock:
ffff88806b638488 (&of->mutex){+.+.}-{3:3}, at: kernfs_seq_start+0x53/0x3b0 fs/kernfs/file.c:154

but task is already holding lock:
ffff88806fe359e0 (&p->lock){+.+.}-{3:3}, at: seq_read_iter+0xb7/0xd60 fs/seq_file.c:182

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&p->lock){+.+.}-{3:3}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
       __mutex_lock_common kernel/locking/mutex.c:608 [inline]
       __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
       seq_read_iter+0xb7/0xd60 fs/seq_file.c:182
       call_read_iter include/linux/fs.h:2104 [inline]
       copy_splice_read+0x662/0xb60 fs/splice.c:365
       do_splice_read fs/splice.c:985 [inline]
       splice_file_to_pipe+0x299/0x500 fs/splice.c:1295
       do_sendfile+0x515/0xdc0 fs/read_write.c:1301
       __do_sys_sendfile64 fs/read_write.c:1362 [inline]
       __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1348
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&pipe->mutex){+.+.}-{3:3}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
       __mutex_lock_common kernel/locking/mutex.c:608 [inline]
       __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
       iter_file_splice_write+0x335/0x14e0 fs/splice.c:687
       do_splice_from fs/splice.c:941 [inline]
       do_splice+0xd77/0x1880 fs/splice.c:1354
       __do_splice fs/splice.c:1436 [inline]
       __do_sys_splice fs/splice.c:1652 [inline]
       __se_sys_splice+0x331/0x4a0 fs/splice.c:1634
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (sb_writers#4){.+.+}-{0:0}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1664 [inline]
       sb_start_write+0x4d/0x1c0 include/linux/fs.h:1800
       mnt_want_write+0x3f/0x90 fs/namespace.c:409
       ovl_create_object+0x13b/0x370 fs/overlayfs/dir.c:629
       lookup_open fs/namei.c:3497 [inline]
       open_last_lookups fs/namei.c:3566 [inline]
       path_openat+0x1425/0x3240 fs/namei.c:3796
       do_filp_open+0x235/0x490 fs/namei.c:3826
       do_sys_openat2+0x13e/0x1d0 fs/open.c:1406
       do_sys_open fs/open.c:1421 [inline]
       __do_sys_openat fs/open.c:1437 [inline]
       __se_sys_openat fs/open.c:1432 [inline]
       __x64_sys_openat+0x247/0x2a0 fs/open.c:1432
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
       down_read+0xb1/0xa40 kernel/locking/rwsem.c:1526
       inode_lock_shared include/linux/fs.h:805 [inline]
       lookup_slow+0x45/0x70 fs/namei.c:1708
       walk_component+0x2e1/0x410 fs/namei.c:2004
       lookup_last fs/namei.c:2461 [inline]
       path_lookupat+0x16f/0x450 fs/namei.c:2485
       filename_lookup+0x256/0x610 fs/namei.c:2514
       kern_path+0x35/0x50 fs/namei.c:2622
       lookup_bdev+0xc5/0x290 block/bdev.c:1136
       resume_store+0x1a0/0x710 kernel/power/hibernate.c:1235
       kernfs_fop_write_iter+0x3a1/0x500 fs/kernfs/file.c:334
       call_write_iter include/linux/fs.h:2110 [inline]
       new_sync_write fs/read_write.c:497 [inline]
       vfs_write+0xa84/0xcb0 fs/read_write.c:590
       ksys_write+0x1a0/0x2c0 fs/read_write.c:643
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&of->mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
       __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
       __mutex_lock_common kernel/locking/mutex.c:608 [inline]
       __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
       kernfs_seq_start+0x53/0x3b0 fs/kernfs/file.c:154
       seq_read_iter+0x3d0/0xd60 fs/seq_file.c:225
       call_read_iter include/linux/fs.h:2104 [inline]
       copy_splice_read+0x662/0xb60 fs/splice.c:365
       do_splice_read fs/splice.c:985 [inline]
       splice_file_to_pipe+0x299/0x500 fs/splice.c:1295
       do_sendfile+0x515/0xdc0 fs/read_write.c:1301
       __do_sys_sendfile64 fs/read_write.c:1362 [inline]
       __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1348
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &of->mutex --> &pipe->mutex --> &p->lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&p->lock);
                               lock(&pipe->mutex);
                               lock(&p->lock);
  lock(&of->mutex);

 *** DEADLOCK ***

2 locks held by syz-executor.1/17062:
 #0: ffff88802d049468 (&pipe->mutex){+.+.}-{3:3}, at: splice_file_to_pipe+0x2e/0x500 fs/splice.c:1292
 #1: ffff88806fe359e0 (&p->lock){+.+.}-{3:3}, at: seq_read_iter+0xb7/0xd60 fs/seq_file.c:182

stack backtrace:
CPU: 0 PID: 17062 Comm: syz-executor.1 Not tainted 6.9.0-rc5-syzkaller-00031-g71b1543c83d6 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
 __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
 __mutex_lock_common kernel/locking/mutex.c:608 [inline]
 __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
 kernfs_seq_start+0x53/0x3b0 fs/kernfs/file.c:154
 seq_read_iter+0x3d0/0xd60 fs/seq_file.c:225
 call_read_iter include/linux/fs.h:2104 [inline]
 copy_splice_read+0x662/0xb60 fs/splice.c:365
 do_splice_read fs/splice.c:985 [inline]
 splice_file_to_pipe+0x299/0x500 fs/splice.c:1295
 do_sendfile+0x515/0xdc0 fs/read_write.c:1301
 __do_sys_sendfile64 fs/read_write.c:1362 [inline]
 __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1348
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f50be67dea9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f50bf41a0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f50be7ac1f0 RCX: 00007f50be67dea9
RDX: 0000000000000000 RSI: 0000000000000007 RDI: 0000000000000005
RBP: 00007f50be6ca4a4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000006e R14: 00007f50be7ac1f0 R15: 00007ffe78344d68
 </TASK>


---
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