possible deadlock in ovl_nlink_start (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e548869f356f Linux 4.14.291
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1353b5bd080000
kernel config: https://syzkaller.appspot.com/x/.config?x=14f65e3c6215eb84
dashboard link: https://syzkaller.appspot.com/bug?extid=18b5b3a932bc565a436d
compiler: gcc version 10.2.1 20210110 (Debian 10.2.1-6)

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+18b5b3...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
4.14.291-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.4/11994 is trying to acquire lock:
(&oi->lock){+.+.}, at: [<ffffffff823150bf>] ovl_nlink_start+0x22f/0x460 fs/overlayfs/util.c:523

but task is already holding lock:
(sb_writers#6){.+.+}, at: [<ffffffff818e03ea>] sb_start_write include/linux/fs.h:1551 [inline]
(sb_writers#6){.+.+}, at: [<ffffffff818e03ea>] mnt_want_write+0x3a/0xb0 fs/namespace.c:386

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (sb_writers#6){.+.+}:
percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36 [inline]
percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
__sb_start_write+0x64/0x260 fs/super.c:1342
sb_start_write include/linux/fs.h:1551 [inline]
mnt_want_write+0x3a/0xb0 fs/namespace.c:386
ovl_create_object+0x75/0x1d0 fs/overlayfs/dir.c:538
lookup_open+0x77a/0x1750 fs/namei.c:3241
do_last fs/namei.c:3334 [inline]
path_openat+0xe08/0x2970 fs/namei.c:3571
do_filp_open+0x179/0x3c0 fs/namei.c:3605
do_sys_open+0x296/0x410 fs/open.c:1081
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb

-> #1 (&ovl_i_mutex_dir_key[depth]#2){++++}:
down_read+0x36/0x80 kernel/locking/rwsem.c:24
inode_lock_shared include/linux/fs.h:729 [inline]
lookup_slow+0x129/0x400 fs/namei.c:1674
lookup_one_len_unlocked+0x3a0/0x410 fs/namei.c:2595
ovl_lower_positive+0x184/0x350 fs/overlayfs/namei.c:783
ovl_rename+0x47c/0xe50 fs/overlayfs/dir.c:968
vfs_rename+0x560/0x1820 fs/namei.c:4498
SYSC_renameat2 fs/namei.c:4646 [inline]
SyS_renameat2+0x95b/0xad0 fs/namei.c:4535
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb

-> #0 (&oi->lock){+.+.}:
lock_acquire+0x170/0x3f0 kernel/locking/lockdep.c:3998
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0xc4/0x1310 kernel/locking/mutex.c:893
ovl_nlink_start+0x22f/0x460 fs/overlayfs/util.c:523
ovl_link+0xee/0x190 fs/overlayfs/dir.c:607
vfs_link+0x6d5/0xb40 fs/namei.c:4266
SYSC_linkat fs/namei.c:4334 [inline]
SyS_linkat+0x3e5/0x6a0 fs/namei.c:4290
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb

other info that might help us debug this:

Chain exists of:
&oi->lock --> &ovl_i_mutex_dir_key[depth]#2 --> sb_writers#6

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(sb_writers#6);
lock(&ovl_i_mutex_dir_key[depth]#2);
lock(sb_writers#6);
lock(&oi->lock);

*** DEADLOCK ***

4 locks held by syz-executor.4/11994:
#0: (sb_writers#14){.+.+}, at: [<ffffffff818e03ea>] sb_start_write include/linux/fs.h:1551 [inline]
#0: (sb_writers#14){.+.+}, at: [<ffffffff818e03ea>] mnt_want_write+0x3a/0xb0 fs/namespace.c:386
#1: (&ovl_i_mutex_dir_key[depth]#2/1){+.+.}, at: [<ffffffff818a7caa>] inode_lock_nested include/linux/fs.h:754 [inline]
#1: (&ovl_i_mutex_dir_key[depth]#2/1){+.+.}, at: [<ffffffff818a7caa>] filename_create+0x12a/0x3f0 fs/namei.c:3676
#2: (&ovl_i_mutex_key[depth]#2){+.+.}, at: [<ffffffff8189a663>] inode_lock include/linux/fs.h:719 [inline]
#2: (&ovl_i_mutex_key[depth]#2){+.+.}, at: [<ffffffff8189a663>] vfs_link+0x553/0xb40 fs/namei.c:4257
#3: (sb_writers#6){.+.+}, at: [<ffffffff818e03ea>] sb_start_write include/linux/fs.h:1551 [inline]
#3: (sb_writers#6){.+.+}, at: [<ffffffff818e03ea>] mnt_want_write+0x3a/0xb0 fs/namespace.c:386

stack backtrace:
CPU: 1 PID: 11994 Comm: syz-executor.4 Not tainted 4.14.291-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x1b2/0x281 lib/dump_stack.c:58
print_circular_bug.constprop.0.cold+0x2d7/0x41e kernel/locking/lockdep.c:1258
check_prev_add kernel/locking/lockdep.c:1905 [inline]
check_prevs_add kernel/locking/lockdep.c:2022 [inline]
validate_chain kernel/locking/lockdep.c:2464 [inline]
__lock_acquire+0x2e0e/0x3f20 kernel/locking/lockdep.c:3491
lock_acquire+0x170/0x3f0 kernel/locking/lockdep.c:3998
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0xc4/0x1310 kernel/locking/mutex.c:893
ovl_nlink_start+0x22f/0x460 fs/overlayfs/util.c:523
ovl_link+0xee/0x190 fs/overlayfs/dir.c:607
vfs_link+0x6d5/0xb40 fs/namei.c:4266
SYSC_linkat fs/namei.c:4334 [inline]
SyS_linkat+0x3e5/0x6a0 fs/namei.c:4290
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7f59f5524279
RSP: 002b:00007f59f3e99168 EFLAGS: 00000246 ORIG_RAX: 0000000000000056
RAX: ffffffffffffffda RBX: 00007f59f5636f80 RCX: 00007f59f5524279
RDX: 0000000000000000 RSI: 0000000020000280 RDI: 0000000020000200
RBP: 00007f59f557e189 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd9699fe7f R14: 00007f59f3e99300 R15: 0000000000022000
EXT4-fs (loop1): inodes count not valid: 7077920 vs 32
unregister_netdevice: waiting for ip6gre0 to become free. Usage count = -1
9pnet: Insufficient options for proto=fd
F2FS-fs (loop4): Invalid log sectors per block(393219) log sectorsize(9)
F2FS-fs (loop4): Can't find valid F2FS filesystem in 1th superblock
F2FS-fs (loop4): invalid crc value
F2FS-fs (loop4): Mounted with checkpoint version = 7ad43cd7
F2FS-fs (loop4): Invalid log sectors per block(393219) log sectorsize(9)
F2FS-fs (loop4): Can't find valid F2FS filesystem in 1th superblock
F2FS-fs (loop4): invalid crc value
F2FS-fs (loop4): Mounted with checkpoint version = 7ad43cd7
F2FS-fs (loop4): Invalid log sectors per block(393219) log sectorsize(9)
F2FS-fs (loop4): Can't find valid F2FS filesystem in 1th superblock
mmap: syz-executor.0 (12390) uses deprecated remap_file_pages() syscall. See Documentation/vm/remap_file_pages.txt.


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.