linux-kernel - Re: [syzbot] [overlayfs?] WARNING in shmem

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Message-ID: <6928e512.a70a0220.d98e3.0124.GAE@google.com>
Date: Thu, 27 Nov 2025 15:56:02 -0800
From: syzbot <syzbot+bfc9a0ccf0de47d04e8c@...kaller.appspotmail.com>
To: amir73il@...il.com, brauner@...nel.org, hdanton@...a.com, 
	linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org, 
	miklos@...redi.hu, neilb@...mail.net, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [overlayfs?] WARNING in shmem_unlink (2)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in shmem_unlink

------------[ cut here ]------------
WARNING: CPU: 1 PID: 6869 at fs/inode.c:417 drop_nlink+0xc5/0x110 fs/inode.c:417
Modules linked in:
CPU: 1 UID: 0 PID: 6869 Comm: syz.0.58 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:drop_nlink+0xc5/0x110 fs/inode.c:417
Code: c0 08 00 00 be 08 00 00 00 e8 37 6a ec ff f0 48 ff 83 c0 08 00 00 5b 41 5c 41 5e 41 5f 5d c3 cc cc cc cc cc e8 0c a6 8a ff 90 <0f> 0b 90 eb 81 44 89 f1 80 e1 07 80 c1 03 38 c1 0f 8c 5b ff ff ff
RSP: 0018:ffffc90003bd7288 EFLAGS: 00010293
RAX: ffffffff82340734 RBX: ffff8880592bec40 RCX: ffff88802957da00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff5200077ae49 R12: 1ffff1100b257d91
R13: 000000006928e4cf R14: ffff8880592bec88 R15: dffffc0000000000
FS:  00007fecf3ad56c0(0000) GS:ffff888126ef4000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fecf3ad4f98 CR3: 0000000039a9c000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 shmem_unlink+0x1f5/0x2d0 mm/shmem.c:3979
 shmem_rename2+0x22d/0x360 mm/shmem.c:4065
 vfs_rename+0xb34/0xe80 fs/namei.c:5216
 ovl_do_rename+0x13c/0x210 fs/overlayfs/overlayfs.h:373
 ovl_create_over_whiteout fs/overlayfs/dir.c:550 [inline]
 ovl_create_or_link+0xaf7/0x1410 fs/overlayfs/dir.c:656
 ovl_create_object+0x234/0x310 fs/overlayfs/dir.c:695
 lookup_open fs/namei.c:3796 [inline]
 open_last_lookups fs/namei.c:3895 [inline]
 path_openat+0x1500/0x3840 fs/namei.c:4131
 do_filp_open+0x1fa/0x410 fs/namei.c:4161
 do_sys_openat2+0x121/0x1c0 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+0x138/0x170 fs/open.c:1463
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fecf448f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fecf3ad5038 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007fecf46e6090 RCX: 00007fecf448f749
RDX: 0000000000105042 RSI: 0000200000000080 RDI: ffffffffffffff9c
RBP: 00007fecf4513f91 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000001ff R11: 0000000000000246 R12: 0000000000000000
R13: 00007fecf46e6128 R14: 00007fecf46e6090 R15: 00007ffc02c45398
 </TASK>


Tested on:

commit:         e1afacb6 Merge tag 'ceph-for-6.18-rc8' of https://gith..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11681f42580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=38a0c4cddc846161
dashboard link: https://syzkaller.appspot.com/bug?extid=bfc9a0ccf0de47d04e8c
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Note: no patches were applied.