syzbot


WARNING in shmem_unlink

Status: upstream: reported syz repro on 2025/08/16 03:08
Subsystems: overlayfs
[Documentation on labels]
Reported-by: syzbot+ec9fab8b7f0386b98a17@syzkaller.appspotmail.com
Fix commit: e8bd877fb76b ovl: fix possible double unlink
Patched on: [ci-qemu-gce-upstream-auto ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-snapshot-upstream-root ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-linux-next-kasan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci-upstream-rust-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb], missing on: [ci-qemu-native-arm64-kvm ci-qemu2-riscv64 ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64]
First crash: 11d, last: 5d00h
Cause bisection: the cause commit could be any of (bisect log):
  241062ae5d87 ovl: change ovl_workdir_cleanup() to take dir lock as needed.
  a45ee87ded78 ovl: narrow locking in ovl_workdir_cleanup_recurse()
  c69566b1d11d ovl: narrow locking on ovl_remove_and_whiteout()
  
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [overlayfs?] WARNING in shmem_unlink 6 (10) 2025/08/18 21:35
Last patch testing requests (3)
Created Duration User Patch Repo Result
2025/08/18 09:17 18m hdanton@sina.com patch upstream OK log
2025/08/17 19:52 0m abinashsinghlalotra@gmail.com patch upstream error
2025/08/16 05:42 18m hdanton@sina.com patch upstream report log

Sample crash report:
------------[ cut here ]------------
WARNING: CPU: 1 PID: 9026 at fs/inode.c:417 drop_nlink+0xc5/0x110 fs/inode.c:417
Modules linked in:
CPU: 1 UID: 0 PID: 9026 Comm: syz.4.1430 Tainted: G        W           6.17.0-rc1-syzkaller-00038-g0cc53520e68b #0 PREEMPT_{RT,(full)} 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:drop_nlink+0xc5/0x110 fs/inode.c:417
Code: c8 08 00 00 be 08 00 00 00 e8 b7 90 ec ff f0 48 ff 83 c8 08 00 00 5b 41 5c 41 5e 41 5f 5d e9 82 9f c8 08 cc e8 dc 5a 8d 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:ffffc9000f5ef600 EFLAGS: 00010293
RAX: ffffffff82310064 RBX: ffff88803352c420 RCX: ffff88802cfcbb80
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff52001ebdeb5 R12: 1ffff110066a588d
R13: 00000000689e7afa R14: ffff88803352c468 R15: dffffc0000000000
FS:  00007fec6bd366c0(0000) GS:ffff8881269c5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555591d73608 CR3: 00000000274f4000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 shmem_unlink+0x1f5/0x2d0 mm/shmem.c:4041
 vfs_unlink+0x39a/0x660 fs/namei.c:4586
 ovl_do_unlink fs/overlayfs/overlayfs.h:218 [inline]
 ovl_cleanup_locked fs/overlayfs/dir.c:36 [inline]
 ovl_cleanup+0x151/0x230 fs/overlayfs/dir.c:56
 ovl_check_rename_whiteout fs/overlayfs/super.c:607 [inline]
 ovl_make_workdir fs/overlayfs/super.c:704 [inline]
 ovl_get_workdir+0xabd/0x17c0 fs/overlayfs/super.c:827
 ovl_fill_super+0x1365/0x35b0 fs/overlayfs/super.c:1406
 vfs_get_super fs/super.c:1325 [inline]
 get_tree_nodev+0xbb/0x150 fs/super.c:1344
 vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
 do_new_mount+0x2a2/0x9e0 fs/namespace.c:3805
 do_mount fs/namespace.c:4133 [inline]
 __do_sys_mount fs/namespace.c:4344 [inline]
 __se_sys_mount+0x317/0x410 fs/namespace.c:4321
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fec6c6cebe9
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:00007fec6bd36038 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fec6c8f5fa0 RCX: 00007fec6c6cebe9
RDX: 0000200000000200 RSI: 0000200000000000 RDI: 0000000000000000
RBP: 00007fec6c751e19 R08: 0000200000000140 R09: 0000000000000000
R10: 00000000000000d4 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fec6c8f6038 R14: 00007fec6c8f5fa0 R15: 00007ffc15eea8d8
 </TASK>

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/08/15 00:17 upstream 0cc53520e68b 5d8c2ac2 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-upstream-fs WARNING in shmem_unlink
2025/08/14 21:14 upstream 0cc53520e68b 5d8c2ac2 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-upstream-fs WARNING in shmem_unlink
2025/08/14 18:49 upstream 0cc53520e68b 5d8c2ac2 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-upstream-fs WARNING in shmem_unlink
2025/08/15 09:31 upstream 24ea63ea3877 1804e95e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs WARNING in shmem_unlink
2025/08/14 16:11 upstream 0cc53520e68b 5d8c2ac2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs WARNING in shmem_unlink
2025/08/21 10:28 upstream 41cd3fd15263 0b9605c8 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream WARNING in shmem_unlink
* Struck through repros no longer work on HEAD.