syzbot


WARNING: refcount bug in blk_done_softirq (2)

Status: upstream: reported C repro on 2024/12/20 13:24
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+cb362dc128596773bb9d@syzkaller.appspotmail.com
First crash: 319d, last: 25d
Bug presence (2)
Date Name Commit Repro Result
2025/10/17 linux-5.15.y (ToT) 29e53a5b1c4f C [report] WARNING: refcount bug in blk_mq_dispatch_rq_list
2025/10/17 upstream (ToT) 6f3b6e91f720 C Didn't crash
Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 WARNING: refcount bug in blk_done_softirq 13 1 834d 834d 0/3 auto-obsoleted due to no activity on 2023/11/01 11:50
Last patch testing requests (4)
Created Duration User Patch Repo Result
2025/10/25 06:36 14m retest repro linux-5.15.y report log
2025/08/13 02:25 12m retest repro linux-5.15.y report log
2025/06/03 12:10 10m retest repro linux-5.15.y report log
2025/03/20 23:37 11m retest repro linux-5.15.y report log
Fix bisection attempts (1)
Created Duration User Patch Repo Result
2025/05/22 08:26 2h01m fix candidate upstream OK (0) job log

Sample crash report:
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 20 at lib/refcount.c:28 refcount_warn_saturate+0x11b/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 20 Comm: ksoftirqd/1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:refcount_warn_saturate+0x11b/0x1a0 lib/refcount.c:28
Code: 09 01 48 c7 c7 e0 67 59 8a e8 d1 91 c3 05 0f 0b eb c4 e8 28 f4 9c fd c6 05 7f 1a 7b 09 01 48 c7 c7 40 68 59 8a e8 b5 91 c3 05 <0f> 0b eb a8 e8 0c f4 9c fd c6 05 60 1a 7b 09 01 48 c7 c7 80 67 59
RSP: 0018:ffffc90000da7c78 EFLAGS: 00010246

RAX: 1708c79c29411400 RBX: 0000000000000003 RCX: ffff888016a90000
RDX: 0000000000000100 RSI: 0000000000000100 RDI: 0000000000000000
RBP: 0000000000000001 R08: dffffc0000000000 R09: fffffbfff1ad32b6
R10: fffffbfff1ad32b6 R11: 1ffffffff1ad32b5 R12: dffffc0000000000
R13: 0000000000000005 R14: 0000000000000003 R15: ffffffff8a7ca320
FS:  0000000000000000(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c006cc3000 CR3: 000000007a5ea000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 blk_complete_reqs block/blk-mq.c:587 [inline]
 blk_done_softirq+0xfa/0x140 block/blk-mq.c:592
 handle_softirqs+0x328/0x820 kernel/softirq.c:576
 run_ksoftirqd+0x98/0xf0 kernel/softirq.c:943
 smpboot_thread_fn+0x4f6/0x970 kernel/smpboot.c:164
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/10/10 16:44 linux-5.15.y 29e53a5b1c4f ff1712fe .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: refcount bug in blk_done_softirq
2025/03/05 06:58 linux-5.15.y c16c81c81336 c3901742 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: refcount bug in blk_done_softirq
2025/03/06 06:20 linux-5.15.y c16c81c81336 831e3629 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: refcount bug in blk_done_softirq
2024/12/20 13:24 linux-5.15.y 91786f140358 0f61b415 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: refcount bug in blk_done_softirq
* Struck through repros no longer work on HEAD.