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Date: Mon, 12 Feb 2024 02:36:24 -0800
Message-ID: <00000000000074c6de06112cd910@google.com>
Subject: [syzbot] [overlayfs?] possible deadlock in seq_read_iter (3)
From: syzbot <syzbot+af9aa785e14a67796a87@syzkaller.appspotmail.com>
To: amir73il@gmail.com, linux-fsdevel@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-unionfs@vger.kernel.org, 
	miklos@szeredi.hu, syzkaller-bugs@googlegroups.com
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Hello,

syzbot found the following issue on:

HEAD commit:    841c35169323 Linux 6.8-rc4
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1215e120180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fbd950b5071b7ea3
dashboard link: https://syzkaller.appspot.com/bug?extid=af9aa785e14a67796a87
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/ef821afd15d3/disk-841c3516.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e41102f18e6e/vmlinux-841c3516.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a17352b259d8/bzImage-841c3516.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+af9aa785e14a67796a87@syzkaller.appspotmail.com

F2FS-fs (loop1): Found nat_bits in checkpoint
F2FS-fs (loop1): Mounted with checkpoint version = 48b305e5
======================================================
WARNING: possible circular locking dependency detected
6.8.0-rc4-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.1/640 is trying to acquire lock:
ffff888072750310 (&p->lock){+.+.}-{3:3}, at: seq_read_iter+0xb7/0xd60 fs/seq_file.c:182

but task is already holding lock:
ffff888023f61c68 (&pipe->mutex/1){+.+.}-{3:3}, at: splice_file_to_pipe+0x2e/0x500 fs/splice.c:1292

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&pipe->mutex/1){+.+.}-{3:3}:
       lock_acquire+0x1e3/0x530 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_64+0xf9/0x240
       entry_SYSCALL_64_after_hwframe+0x6f/0x77

-> #3 (sb_writers#4){.+.+}-{0:0}:
       lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1639 [inline]
       sb_start_write+0x4d/0x1c0 include/linux/fs.h:1775
       mnt_want_write+0x3f/0x90 fs/namespace.c:409
       ovl_fix_origin fs/overlayfs/namei.c:908 [inline]
       ovl_lookup+0x1394/0x2a60 fs/overlayfs/namei.c:1143
       __lookup_slow+0x28c/0x3f0 fs/namei.c:1693
       lookup_slow+0x53/0x70 fs/namei.c:1710
       walk_component fs/namei.c:2001 [inline]
       link_path_walk+0x9cd/0xe80 fs/namei.c:2328
       path_lookupat+0xa9/0x450 fs/namei.c:2481
       filename_lookup+0x255/0x610 fs/namei.c:2511
       user_path_at_empty+0x42/0x60 fs/namei.c:2920
       user_path_at include/linux/namei.h:57 [inline]
       __do_sys_chdir fs/open.c:556 [inline]
       __se_sys_chdir+0xbf/0x220 fs/open.c:550
       do_syscall_64+0xf9/0x240
       entry_SYSCALL_64_after_hwframe+0x6f/0x77

-> #2 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}:
       lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
       down_read+0xb1/0xa40 kernel/locking/rwsem.c:1526
       inode_lock_shared include/linux/fs.h:812 [inline]
       lookup_slow+0x45/0x70 fs/namei.c:1709
       walk_component+0x2e1/0x410 fs/namei.c:2001
       lookup_last fs/namei.c:2458 [inline]
       path_lookupat+0x16f/0x450 fs/namei.c:2482
       filename_lookup+0x255/0x610 fs/namei.c:2511
       kern_path+0x35/0x50 fs/namei.c:2619
       lookup_bdev+0xc5/0x290 block/bdev.c:1014
       resume_store+0x1a0/0x710 kernel/power/hibernate.c:1183
       kernfs_fop_write_iter+0x3a4/0x500 fs/kernfs/file.c:334
       call_write_iter include/linux/fs.h:2085 [inline]
       new_sync_write fs/read_write.c:497 [inline]
       vfs_write+0xa81/0xcb0 fs/read_write.c:590
       ksys_write+0x1a0/0x2c0 fs/read_write.c:643
       do_syscall_64+0xf9/0x240
       entry_SYSCALL_64_after_hwframe+0x6f/0x77

-> #1 (&of->mutex){+.+.}-{3:3}:
       lock_acquire+0x1e3/0x530 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:2079 [inline]
       new_sync_read fs/read_write.c:395 [inline]
       vfs_read+0x978/0xb70 fs/read_write.c:476
       ksys_read+0x1a0/0x2c0 fs/read_write.c:619
       do_syscall_64+0xf9/0x240
       entry_SYSCALL_64_after_hwframe+0x6f/0x77

-> #0 (&p->lock){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain+0x18ca/0x58e0 kernel/locking/lockdep.c:3869
       __lock_acquire+0x1345/0x1fd0 kernel/locking/lockdep.c:5137
       lock_acquire+0x1e3/0x530 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
       proc_reg_read_iter+0x1c3/0x290 fs/proc/inode.c:302
       call_read_iter include/linux/fs.h:2079 [inline]
       copy_splice_read+0x661/0xb60 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:1356 [inline]
       __se_sys_sendfile64+0x100/0x1e0 fs/read_write.c:1348
       do_syscall_64+0xf9/0x240
       entry_SYSCALL_64_after_hwframe+0x6f/0x77

other info that might help us debug this:

Chain exists of:
  &p->lock --> sb_writers#4 --> &pipe->mutex/1

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&pipe->mutex/1);
                               lock(sb_writers#4);
                               lock(&pipe->mutex/1);
  lock(&p->lock);

 *** DEADLOCK ***

1 lock held by syz-executor.1/640:
 #0: ffff888023f61c68 (&pipe->mutex/1){+.+.}-{3:3}, at: splice_file_to_pipe+0x2e/0x500 fs/splice.c:1292

stack backtrace:
CPU: 1 PID: 640 Comm: syz-executor.1 Not tainted 6.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2e0 lib/dump_stack.c:106
 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+0x18ca/0x58e0 kernel/locking/lockdep.c:3869
 __lock_acquire+0x1345/0x1fd0 kernel/locking/lockdep.c:5137
 lock_acquire+0x1e3/0x530 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
 proc_reg_read_iter+0x1c3/0x290 fs/proc/inode.c:302
 call_read_iter include/linux/fs.h:2079 [inline]
 copy_splice_read+0x661/0xb60 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:1356 [inline]
 __se_sys_sendfile64+0x100/0x1e0 fs/read_write.c:1348
 do_syscall_64+0xf9/0x240
 entry_SYSCALL_64_after_hwframe+0x6f/0x77
RIP: 0033:0x7f3acde7dda9
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:00007f3acec5e0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f3acdfac050 RCX: 00007f3acde7dda9
RDX: 0000000020000000 RSI: 0000000000000004 RDI: 0000000000000000
RBP: 00007f3acdeca47a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000007 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f3acdfac050 R15: 00007fff9463d788
 </TASK>


---
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