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* [syzbot] [kernfs?] possible deadlock in mnt_want_write (3)
@ 2024-01-01  7:31 syzbot
  0 siblings, 0 replies; only message in thread
From: syzbot @ 2024-01-01  7:31 UTC (permalink / raw)
  To: gregkh, linux-fsdevel, linux-kernel, syzkaller-bugs, tj

Hello,

syzbot found the following issue on:

HEAD commit:    453f5db0619e Merge tag 'trace-v6.7-rc7' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1011351de80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f8e72bae38c079e4
dashboard link: https://syzkaller.appspot.com/bug?extid=3800901c18018cf7ff68
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/38b92a7149e8/disk-453f5db0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4f872267133f/vmlinux-453f5db0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/587572061791/bzImage-453f5db0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3800901c18018cf7ff68@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.7.0-rc7-syzkaller-00049-g453f5db0619e #0 Not tainted
------------------------------------------------------
syz-executor.4/5849 is trying to acquire lock:
ffff88814c8dc418 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:404

but task is already holding lock:
ffff88807d50efe0 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: inode_lock include/linux/fs.h:802 [inline]
ffff88807d50efe0 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: open_last_lookups fs/namei.c:3543 [inline]
ffff88807d50efe0 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: path_openat+0x7bc/0x3290 fs/namei.c:3776

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&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
       call_write_iter include/linux/fs.h:2020 [inline]
       new_sync_write fs/read_write.c:491 [inline]
       vfs_write+0x792/0xb20 fs/read_write.c:584
       ksys_write+0x1a0/0x2c0 fs/read_write.c:637
       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 (&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

-> #1 (&p->lock){+.+.}-{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
       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

-> #0 (sb_writers#4){.+.+}-{0:0}:
       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
       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_openat fs/open.c:1468 [inline]
       __se_sys_openat fs/open.c:1463 [inline]
       __x64_sys_openat+0x247/0x290 fs/open.c:1463
       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:
  sb_writers#4 --> &of->mutex --> &ovl_i_mutex_dir_key[depth]

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by syz-executor.4/5849:
 #0: ffff888079772418 (sb_writers#28){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:404
 #1: ffff88807d50efe0 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: inode_lock include/linux/fs.h:802 [inline]
 #1: ffff88807d50efe0 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: open_last_lookups fs/namei.c:3543 [inline]
 #1: ffff88807d50efe0 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: path_openat+0x7bc/0x3290 fs/namei.c:3776

stack backtrace:
CPU: 0 PID: 5849 Comm: syz-executor.4 Not tainted 6.7.0-rc7-syzkaller-00049-g453f5db0619e #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
 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_openat fs/open.c:1468 [inline]
 __se_sys_openat fs/open.c:1463 [inline]
 __x64_sys_openat+0x247/0x290 fs/open.c:1463
 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: 0033:0x7fa7b5a7cce9
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:00007fa7b686b0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007fa7b5b9bf80 RCX: 00007fa7b5a7cce9
RDX: 0000000000141842 RSI: 0000000020000440 RDI: ffffffffffffff9c
RBP: 00007fa7b5ac947a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007fa7b5b9bf80 R15: 00007ffec2fc2058
 </TASK>


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2024-01-01  7:31 [syzbot] [kernfs?] possible deadlock in mnt_want_write (3) syzbot

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