syzbot


possible deadlock in mnt_want_write (3)

Status: upstream: reported on 2024/01/01 07:31
Subsystems: kernfs
[Documentation on labels]
Reported-by: syzbot+3800901c18018cf7ff68@syzkaller.appspotmail.com
First crash: 115d, last: 7d21h
Discussions (2)
Title Replies (including bot) Last reply
[syzbot] Monthly kernfs report (Apr 2024) 0 (1) 2024/04/08 08:30
[syzbot] [kernfs?] possible deadlock in mnt_want_write (3) 0 (1) 2024/01/01 07:31
Similar bugs (7)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 possible deadlock in mnt_want_write origin:upstream missing-backport C done 117 144d 396d 0/3 upstream: reported C repro on 2023/03/21 10:01
upstream possible deadlock in mnt_want_write fs C done done 662 1291d 2098d 15/26 fixed on 2020/11/16 12:12
linux-6.1 possible deadlock in mnt_want_write origin:upstream missing-backport C done 56 145d 389d 0/3 upstream: reported C repro on 2023/03/28 13:05
linux-4.19 possible deadlock in mnt_want_write romfs C 730 411d 1828d 0/1 upstream: reported C repro on 2019/04/19 16:54
android-49 possible deadlock in mnt_want_write 1 2081d 2081d 0/3 auto-closed as invalid on 2019/02/22 14:57
upstream possible deadlock in mnt_want_write (2) integrity overlayfs C done 867 172d 1040d 25/26 fixed on 2023/12/21 01:43
linux-4.14 possible deadlock in mnt_want_write ubifs C 10467 411d 1823d 0/1 upstream: reported C repro on 2019/04/25 05:09

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
6.8.0-syzkaller-08951-gfe46a7dd189e #0 Not tainted
------------------------------------------------------
syz-executor.4/7644 is trying to acquire lock:
ffff88802fedc420 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:409

but task is already holding lock:
ffff888064d3cd00 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: inode_lock include/linux/fs.h:793 [inline]
ffff888064d3cd00 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: open_last_lookups fs/namei.c:3563 [inline]
ffff888064d3cd00 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: path_openat+0x7d3/0x3240 fs/namei.c:3796

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}:
       lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
       down_read+0xb1/0xa40 kernel/locking/rwsem.c:1526
       inode_lock_shared include/linux/fs.h:803 [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:1072
       resume_store+0x1a0/0x710 kernel/power/hibernate.c:1235
       kernfs_fop_write_iter+0x3a4/0x500 fs/kernfs/file.c:334
       call_write_iter include/linux/fs.h:2108 [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_64+0xfb/0x240
       entry_SYSCALL_64_after_hwframe+0x6d/0x75

-> #3 (&of->mutex){+.+.}-{3:3}:
       lock_acquire+0x1e4/0x530 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:2102 [inline]
       new_sync_read fs/read_write.c:395 [inline]
       vfs_read+0x97b/0xb70 fs/read_write.c:476
       ksys_read+0x1a0/0x2c0 fs/read_write.c:619
       do_syscall_64+0xfb/0x240
       entry_SYSCALL_64_after_hwframe+0x6d/0x75

-> #2 (&p->lock){+.+.}-{3:3}:
       lock_acquire+0x1e4/0x530 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
       call_read_iter include/linux/fs.h:2102 [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_64+0xfb/0x240
       entry_SYSCALL_64_after_hwframe+0x6d/0x75

-> #1 (&pipe->mutex){+.+.}-{3:3}:
       lock_acquire+0x1e4/0x530 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+0xfb/0x240
       entry_SYSCALL_64_after_hwframe+0x6d/0x75

-> #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+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
       __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
       lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1662 [inline]
       sb_start_write+0x4d/0x1c0 include/linux/fs.h:1798
       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_64+0xfb/0x240
       entry_SYSCALL_64_after_hwframe+0x6d/0x75

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.4/7644:
 #0: ffff88802371a420 (sb_writers#30){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:409
 #1: ffff888064d3cd00 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: inode_lock include/linux/fs.h:793 [inline]
 #1: ffff888064d3cd00 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: open_last_lookups fs/namei.c:3563 [inline]
 #1: ffff888064d3cd00 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}, at: path_openat+0x7d3/0x3240 fs/namei.c:3796

stack backtrace:
CPU: 0 PID: 7644 Comm: syz-executor.4 Not tainted 6.8.0-syzkaller-08951-gfe46a7dd189e #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+0x1e4/0x530 kernel/locking/lockdep.c:5754
 percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
 __sb_start_write include/linux/fs.h:1662 [inline]
 sb_start_write+0x4d/0x1c0 include/linux/fs.h:1798
 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_64+0xfb/0x240
 entry_SYSCALL_64_after_hwframe+0x6d/0x75
RIP: 0033:0x7f6740e7de69
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:00007f6741bdb0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f6740fabf80 RCX: 00007f6740e7de69
RDX: 000000000000275a RSI: 0000000020000040 RDI: ffffffffffffff9c
RBP: 00007f6740eca47a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f6740fabf80 R15: 00007ffed8acdc28
 </TASK>

Crashes (9):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2024/04/13 10:45 upstream fe46a7dd189e c8349e48 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in mnt_want_write
2024/04/09 04:21 upstream fe46a7dd189e f3234354 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in mnt_want_write
2024/04/05 01:15 upstream fe46a7dd189e 0ee3535e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in mnt_want_write
2024/04/05 00:22 upstream fe46a7dd189e 0ee3535e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in mnt_want_write
2024/04/04 20:15 upstream fe46a7dd189e 0ee3535e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in mnt_want_write
2024/04/04 18:23 upstream fe46a7dd189e 0ee3535e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in mnt_want_write
2024/03/09 12:36 upstream 10d48d70e82d 6ee49f2e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in mnt_want_write
2023/12/31 07:32 upstream 453f5db0619e fb427a07 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in mnt_want_write
2023/12/28 07:28 upstream f5837722ffec fb427a07 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in mnt_want_write
* Struck through repros no longer work on HEAD.