linux-kernel - [syzbot] [fuse?] WARNING: refcount bug in process_scheduled

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Message-ID: <68894408.a00a0220.26d0e1.0012.GAE@google.com>
Date: Tue, 29 Jul 2025 14:58:32 -0700
From: syzbot <syzbot+9921e319bd6168140b40@...kaller.appspotmail.com>
To: andrew.cooper3@...rix.com, bp@...en8.de, brgerst@...il.com, 
	dave.hansen@...ux.intel.com, hpa@...or.com, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org, miklos@...redi.hu, 
	mingo@...hat.com, peterz@...radead.org, song@...nel.org, 
	syzkaller-bugs@...glegroups.com, tglx@...utronix.de, x86@...nel.org, 
	xni@...hat.com, yukuai3@...wei.com
Subject: [syzbot] [fuse?] WARNING: refcount bug in process_scheduled_works

Hello,

syzbot found the following issue on:

HEAD commit:    ced1b9e0392d Merge tag 'ata-6.17-rc1' of git://git.kernel...
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=15c89782580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d51af648924b64c9
dashboard link: https://syzkaller.appspot.com/bug?extid=9921e319bd6168140b40
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=177f7034580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=165e44a2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f1495c1de592/disk-ced1b9e0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/982f755305ce/vmlinux-ced1b9e0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b17cd424f373/bzImage-ced1b9e0.xz

The issue was bisected to:

commit 9e59d609763f70a992a8f3808dabcce60f14eb5c
Author: Xiao Ni <xni@...hat.com>
Date:   Wed Jun 11 07:31:06 2025 +0000

    md: call del_gendisk in control path

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14ab54a2580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=16ab54a2580000
console output: https://syzkaller.appspot.com/x/log.txt?x=12ab54a2580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9921e319bd6168140b40@...kaller.appspotmail.com
Fixes: 9e59d609763f ("md: call del_gendisk in control path")

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 24 at lib/refcount.c:28 refcount_warn_saturate+0x11a/0x1d0 lib/refcount.c:28
Modules linked in:
CPU: 1 UID: 0 PID: 24 Comm: kworker/1:0 Not tainted 6.16.0-syzkaller-00857-gced1b9e0392d #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: md_misc mddev_delayed_delete
RIP: 0010:refcount_warn_saturate+0x11a/0x1d0 lib/refcount.c:28
Code: 00 83 e2 8b e8 b7 5b bf fc 90 0f 0b 90 90 eb d7 e8 bb 6d fb fc c6 05 09 32 c7 0a 01 90 48 c7 c7 60 83 e2 8b e8 97 5b bf fc 90 <0f> 0b 90 90 eb b7 e8 9b 6d fb fc c6 05 e6 31 c7 0a 01 90 48 c7 c7
RSP: 0018:ffffc900001e7a68 EFLAGS: 00010246
RAX: 3c6a9b38a742a100 RBX: 0000000000000003 RCX: ffff88801d298000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: ffffc900001e7c70 R08: ffff8880b8724293 R09: 1ffff110170e4852
R10: dffffc0000000000 R11: ffffed10170e4853 R12: ffff8880b8739700
R13: ffff88801d2ab218 R14: ffff8880331dc130 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff888125d07000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056071c71c048 CR3: 000000000df38000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
 kthread+0x711/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


---
This report is generated by a bot. It may contain errors.
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
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