From: syzbot <syzbot+7c4b3d05083880a09cdd@syzkaller.appspotmail.com>
To: amir73il@gmail.com, linux-kernel@vger.kernel.org,
linux-unionfs@vger.kernel.org, miklos@szeredi.hu,
syzkaller-bugs@googlegroups.com
Subject: [syzbot] [overlayfs?] possible deadlock in iterate_dir (4)
Date: Fri, 02 Oct 2026 13:11:30 -0700 [thread overview]
Message-ID: <6ac00ff2.9ad129c8.3858c0.0004.GAE@google.com> (raw)
Hello,
syzbot found the following issue on:
HEAD commit: 6474fa070f2b Add linux-next specific files for 20260929
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11744725580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3477d5a04d788556
dashboard link: https://syzkaller.appspot.com/bug?extid=7c4b3d05083880a09cdd
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0b184b600605/disk-6474fa07.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/71aa06781faf/vmlinux-6474fa07.xz
kernel image: https://storage.googleapis.com/syzbot-assets/250dcdc25f2b/bzImage-6474fa07.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7c4b3d05083880a09cdd@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.241/6613 is trying to acquire lock:
ffff888079d74140 (&type->i_mutex_dir_key#4){++++}-{4:4}, at: iterate_dir+0x209/0x4d0 fs/readdir.c:103
but task is already holding lock:
ffff888059293d88 (&ovl_i_mutex_dir_key[depth]#2){++++}-{4:4}, at: wrap_directory_iterator+0x5a/0xe0 fs/readdir.c:56
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&ovl_i_mutex_dir_key[depth]#2){++++}-{4:4}:
down_read+0x45/0x320 kernel/locking/rwsem.c:1574
inode_lock_shared include/linux/fs.h:1039 [inline]
lookup_slow+0x46/0x80 fs/namei.c:1935
ovl_lookup_positive_unlocked fs/overlayfs/namei.c:216 [inline]
ovl_lookup_single+0x323/0xe90 fs/overlayfs/namei.c:260
ovl_lookup_layer+0x377/0x440 fs/overlayfs/namei.c:365
ovl_lookup_layers fs/overlayfs/namei.c:1168 [inline]
ovl_lookup+0x9ae/0x1c80 fs/overlayfs/namei.c:1403
lookup_open+0x94b/0x1970 fs/namei.c:4530
open_last_lookups fs/namei.c:4769 [inline]
path_openat+0x673/0x1da0 fs/namei.c:5008
do_file_open+0x23e/0x4a0 fs/namei.c:5040
do_sys_openat2+0x115/0x200 fs/open.c:1442
do_sys_open fs/open.c:1448 [inline]
__do_sys_openat fs/open.c:1464 [inline]
__se_sys_openat fs/open.c:1459 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1459
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #1 (DCACHE_PAR_LOOKUP){+.+.}-{0:0}:
d_wait_lookup fs/dcache.c:2838 [inline]
__d_alloc_parallel+0xc32/0x1700 fs/dcache.c:2942
__lookup_slow+0x82/0x2f0 fs/namei.c:1904
lookup_slow+0x59/0x80 fs/namei.c:1936
walk_component fs/namei.c:2282 [inline]
lookup_last fs/namei.c:2789 [inline]
path_lookupat+0x3f5/0x8c0 fs/namei.c:2813
filename_lookup+0x265/0x5d0 fs/namei.c:2842
do_readlinkat+0xe3/0x510 fs/stat.c:571
__do_sys_readlink fs/stat.c:605 [inline]
__se_sys_readlink fs/stat.c:602 [inline]
__x64_sys_readlink+0x7f/0x90 fs/stat.c:602
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&type->i_mutex_dir_key#4){++++}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3209 [inline]
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
down_read_killable+0x4b/0x3b0 kernel/locking/rwsem.c:1599
iterate_dir+0x209/0x4d0 fs/readdir.c:103
ovl_dir_read+0x141/0x4a0 fs/overlayfs/readdir.c:388
ovl_dir_read_merged+0x2fb/0x520 fs/overlayfs/readdir.c:451
ovl_cache_get fs/overlayfs/readdir.c:504 [inline]
ovl_iterate_merged fs/overlayfs/readdir.c:846 [inline]
ovl_iterate+0xd5a/0x2160 fs/overlayfs/readdir.c:906
wrap_directory_iterator+0x96/0xe0 fs/readdir.c:67
iterate_dir+0x2e2/0x4d0 fs/readdir.c:110
__do_sys_getdents64 fs/readdir.c:399 [inline]
__se_sys_getdents64+0xf1/0x280 fs/readdir.c:384
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Chain exists of:
&type->i_mutex_dir_key#4 --> DCACHE_PAR_LOOKUP --> &ovl_i_mutex_dir_key[depth]#2
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&ovl_i_mutex_dir_key[depth]#2);
lock(DCACHE_PAR_LOOKUP);
lock(&ovl_i_mutex_dir_key[depth]#2);
rlock(&type->i_mutex_dir_key#4);
*** DEADLOCK ***
locks held by syz.1.241/6613: 2, last CPU#1:
#0: ffff88807eb65cf0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x118/0x160 fs/file.c:1408
#1: ffff888059293d88 (&ovl_i_mutex_dir_key[depth]#2){++++}-{4:4}, at: wrap_directory_iterator+0x5a/0xe0 fs/readdir.c:56
stack backtrace:
CPU: 1 UID: 0 PID: 6613 Comm: syz.1.241 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
check_prev_add kernel/locking/lockdep.c:3209 [inline]
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
down_read_killable+0x4b/0x3b0 kernel/locking/rwsem.c:1599
iterate_dir+0x209/0x4d0 fs/readdir.c:103
ovl_dir_read+0x141/0x4a0 fs/overlayfs/readdir.c:388
ovl_dir_read_merged+0x2fb/0x520 fs/overlayfs/readdir.c:451
ovl_cache_get fs/overlayfs/readdir.c:504 [inline]
ovl_iterate_merged fs/overlayfs/readdir.c:846 [inline]
ovl_iterate+0xd5a/0x2160 fs/overlayfs/readdir.c:906
wrap_directory_iterator+0x96/0xe0 fs/readdir.c:67
iterate_dir+0x2e2/0x4d0 fs/readdir.c:110
__do_sys_getdents64 fs/readdir.c:399 [inline]
__se_sys_getdents64+0xf1/0x280 fs/readdir.c:384
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5cfbb9e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5cfc9c0028 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007f5cfbe25fa0 RCX: 00007f5cfbb9e159
RDX: 0000000000001000 RSI: 0000200000001dc0 RDI: 0000000000000009
RBP: 00007f5cfbc3506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5cfbe26038 R14: 00007f5cfbe25fa0 R15: 00007ffe433bef38
</TASK>
---
This report is generated by a bot. It may contain errors.
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reply other threads:[~2026-10-02 20:11 UTC|newest]
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