Message-ID: <0000000000008efd70060ce21487@google.com>
Date: Tue, 19 Dec 2023 11:43:27 -0800
From: syzbot <syzbot+da4f9f61f96525c62cc7@...kaller.appspotmail.com>
To: amir73il@...il.com, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org, 
	miklos@...redi.hu, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [overlayfs?] possible deadlock in seq_read_iter (2)

syzbot has found a reproducer for the following issue on:

HEAD commit:    2cf4f94d8e86 Merge tag 'scsi-fixes' of git://git.kernel.or..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=12181571e80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e5751b3a2226135d
dashboard link: https://syzkaller.appspot.com/bug?extid=da4f9f61f96525c62cc7
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=176a4f49e80000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=154aa8d6e80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cc8943b61205/disk-2cf4f94d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8b515b02658d/vmlinux-2cf4f94d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1f8ccc925248/bzImage-2cf4f94d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+da4f9f61f96525c62cc7@...kaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.7.0-rc6-syzkaller-00010-g2cf4f94d8e86 #0 Not tainted
------------------------------------------------------
syz-executor424/7758 is trying to acquire lock:
ffff88801f1ef9e0 (&p->lock){+.+.}-{3:3}, at: seq_read_iter+0xb2/0xd10 fs/seq_file.c:182

but task is already holding lock:
ffff88814cd7a418 (sb_writers#4){.+.+}-{0:0}, at: do_sendfile+0x607/0x1000 fs/read_write.c:1253

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #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:1635 [inline]
       sb_start_write+0x4d/0x1c0 include/linux/fs.h:1710
       mnt_want_write+0x3f/0x90 fs/namespace.c:404
       ovl_create_object+0x13b/0x360 fs/overlayfs/dir.c:629
       lookup_open fs/namei.c:3477 [inline]
       open_last_lookups fs/namei.c:3546 [inline]
       path_openat+0x13fa/0x3290 fs/namei.c:3776
       do_filp_open+0x234/0x490 fs/namei.c:3809
       do_sys_openat2+0x13e/0x1d0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_open fs/open.c:1460 [inline]
       __se_sys_open fs/open.c:1456 [inline]
       __x64_sys_open+0x225/0x270 fs/open.c:1456
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0x45/0x110 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x63/0x6b

-> #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:1710
       walk_component+0x2d0/0x400 fs/namei.c:2002
       lookup_last fs/namei.c:2459 [inline]
       path_lookupat+0x16f/0x450 fs/namei.c:2483
       filename_lookup+0x255/0x610 fs/namei.c:2512
       kern_path+0x35/0x50 fs/namei.c:2610
       lookup_bdev+0xc5/0x290 block/bdev.c:979
       resume_store+0x1a0/0x710 kernel/power/hibernate.c:1177
       kernfs_fop_write_iter+0x3b3/0x510 fs/kernfs/file.c:334
       do_iter_readv_writev+0x330/0x4a0
       do_iter_write+0x1f6/0x8d0 fs/read_write.c:860
       iter_file_splice_write+0x86d/0x1010 fs/splice.c:736
       do_splice_from fs/splice.c:933 [inline]
       direct_splice_actor+0xea/0x1c0 fs/splice.c:1142
       splice_direct_to_actor+0x376/0x9e0 fs/splice.c:1088
       do_splice_direct+0x2ac/0x3f0 fs/splice.c:1194
       do_sendfile+0x62c/0x1000 fs/read_write.c:1254
       __do_sys_sendfile64 fs/read_write.c:1322 [inline]
       __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1308
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0x45/0x110 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x63/0x6b

-> #1 (&of->mutex){+.+.}-{3:3}:
       lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x136/0xd60 kernel/locking/mutex.c:747
       kernfs_seq_start+0x53/0x3a0 fs/kernfs/file.c:154
       seq_read_iter+0x3d4/0xd10 fs/seq_file.c:225
       call_read_iter include/linux/fs.h:2014 [inline]
       new_sync_read fs/read_write.c:389 [inline]
       vfs_read+0x78b/0xb00 fs/read_write.c:470
       ksys_read+0x1a0/0x2c0 fs/read_write.c:613
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0x45/0x110 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x63/0x6b

-> #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+0x1909/0x5ab0 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:603 [inline]
       __mutex_lock+0x136/0xd60 kernel/locking/mutex.c:747
       seq_read_iter+0xb2/0xd10 fs/seq_file.c:182
       call_read_iter include/linux/fs.h:2014 [inline]
       copy_splice_read+0x4c9/0x9c0 fs/splice.c:364
       splice_direct_to_actor+0x2c4/0x9e0 fs/splice.c:1069
       do_splice_direct+0x2ac/0x3f0 fs/splice.c:1194
       do_sendfile+0x62c/0x1000 fs/read_write.c:1254
       __do_sys_sendfile64 fs/read_write.c:1322 [inline]
       __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1308
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0x45/0x110 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x63/0x6b

other info that might help us debug this:

Chain exists of:
  &p->lock --> &ovl_i_mutex_dir_key[depth] --> sb_writers#4

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(sb_writers#4);
                               lock(&ovl_i_mutex_dir_key[depth]);
                               lock(sb_writers#4);
  lock(&p->lock);

 *** DEADLOCK ***

1 lock held by syz-executor424/7758:
 #0: ffff88814cd7a418 (sb_writers#4){.+.+}-{0:0}, at: do_sendfile+0x607/0x1000 fs/read_write.c:1253

stack backtrace:
CPU: 0 PID: 7758 Comm: syz-executor424 Not tainted 6.7.0-rc6-syzkaller-00010-g2cf4f94d8e86 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
 check_noncircular+0x366/0x490 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+0x1909/0x5ab0 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:603 [inline]
 __mutex_lock+0x136/0xd60 kernel/locking/mutex.c:747
 seq_read_iter+0xb2/0xd10 fs/seq_file.c:182
 call_read_iter include/linux/fs.h:2014 [inline]
 copy_splice_read+0x4c9/0x9c0 fs/splice.c:364
 splice_direct_to_actor+0x2c4/0x9e0 fs/splice.c:1069
 do_splice_direct+0x2ac/0x3f0 fs/splice.c:1194
 do_sendfile+0x62c/0x1000 fs/read_write.c:1254
 __do_sys_sendfile64 fs/read_write.c:1322 [inline]
 __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1308
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x45/0x110 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7fef41211d49
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 81 18 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:00007fef411d2218 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007fef4129c3e8 RCX: 00007fef41211d49
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000003
RBP: 00007fef4129c3e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0001000000201007 R11: 0000000000000246 R12: 00007fef41269060
R13: 0030656c69662f2e R14: 6e6f3d6f6e69782c R15: 0079616c7265766f
 </TASK>


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

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