[syzbot] [block?] BUG: corrupted list in blk_mq_request_bypass_insert

[syzbot] [block?] BUG: corrupted list in blk_mq_request_bypass_insert

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f1b8fa82cab7 Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=14f18379580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d1128bc53f2ef7f3
dashboard link: https://syzkaller.appspot.com/bug?extid=f4353e96f7004ae5a09e
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/932d85a2bda2/disk-f1b8fa82.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5b6b8fb76e8d/vmlinux-f1b8fa82.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c246b61ee396/Image-f1b8fa82.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f4353e96f7004ae5a09e@syzkaller.appspotmail.com

 non-slab/vmalloc memory
list_add corruption. prev->next should be next (ffff0000c8a39040), but was ffff0000c8ab0e48. (prev=ffff0000c8ab0e48).
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:34!
Internal error: Oops - BUG: 00000000f2000800 [#1]  SMP
Modules linked in:
CPU: 0 UID: 0 PID: 4390 Comm: kworker/0:1H Tainted: G             L      syzkaller #0 PREEMPT 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/07/2026
Workqueue: kblockd blk_mq_requeue_work
pstate: 63400005 (nZCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : __list_add_valid_or_report+0x144/0x148 lib/list_debug.c:32
lr : __list_add_valid_or_report+0x144/0x148 lib/list_debug.c:32
sp : ffff8000947079f0
x29: ffff8000947079f0 x28: ffff800094707aa8 x27: ffff800094707aa0
x26: 1fffe00019147209 x25: ffff0000c8a39040 x24: ffff0000c8a39048
x23: 1fffe000191561c9 x22: dfff800000000000 x21: ffff0000c8ab0e48
x20: ffff0000c8ab0e48 x19: ffff0000c8a39040 x18: 1fffe00034bb7428
x17: 3034303933613863 x16: 3030303066666666 x15: 28207478656e2065
x14: 6220646c756f6873 x13: 0000000000000001 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000002 x9 : d55a73c626cee600
x8 : d55a73c626cee600 x7 : ffff80008048c60c x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff80008049731c
x2 : 0000000100000001 x1 : ffff0000c56f3a80 x0 : 0000000000000075
Call trace:
 __list_add_valid_or_report+0x144/0x148 lib/list_debug.c:32 (P)
 __list_add_valid include/linux/list.h:96 [inline]
 __list_add include/linux/list.h:158 [inline]
 list_add_tail include/linux/list.h:191 [inline]
 blk_mq_request_bypass_insert+0x130/0x1cc block/blk-mq.c:2551
 blk_mq_requeue_work+0x3a4/0x52c block/blk-mq.c:1560
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0x788/0x10b8 kernel/workqueue.c:3405
 worker_thread+0x798/0xbd0 kernel/workqueue.c:3486
 kthread+0x304/0x3d4 kernel/kthread.c:436
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:838
Code: 91270000 aa1303e1 aa1403e3 979c2c73 (d4210000) 
---[ end trace 0000000000000000 ]---


---
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Re: [syzbot] [block?] BUG: corrupted list in blk_mq_request_bypass_insert

[Bart Van Assche]

On 8/28/26 10:31 PM, syzbot wrote:
> kernel BUG at lib/list_debug.c:34!
> Call trace:
>   __list_add_valid_or_report+0x144/0x148 lib/list_debug.c:32 (P)
>   __list_add_valid include/linux/list.h:96 [inline]
>   __list_add include/linux/list.h:158 [inline]
>   list_add_tail include/linux/list.h:191 [inline]
>   blk_mq_request_bypass_insert+0x130/0x1cc block/blk-mq.c:2551
>   blk_mq_requeue_work+0x3a4/0x52c block/blk-mq.c:1560
>   process_one_work kernel/workqueue.c:3322 [inline]
>   process_scheduled_works+0x788/0x10b8 kernel/workqueue.c:3405
>   worker_thread+0x798/0xbd0 kernel/workqueue.c:3486
>   kthread+0x304/0x3d4 kernel/kthread.c:436
>   ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:838

If my AI assistant got it right the root cause of this issue is as
follows (I haven't tried to verify this):
* Concurrent calls of nvme_reset_work() and blk_mq_requeue_work().
* nvme_decide_disposition() does not check NVME_REQ_CANCELLED for
   non-multipath requests and returns RETRY instead of COMPLETE.

The same AI assistant proposes the following patch (again, I have not
verified whether this makes sense):

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 8e45a2789123..a1b2c3d4e5f6 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -425,7 +425,8 @@ static inline enum nvme_disposition 
nvme_decide_disposition(struct request *req)
  		if (nvme_is_path_error(nvme_req(req)->status) ||
  		    blk_queue_dying(req->q))
  			return FAILOVER;
  	} else {
-		if (blk_queue_dying(req->q))
+		if (blk_queue_dying(req->q) ||
+		    (nvme_req(req)->flags & NVME_REQ_CANCELLED))
  			return COMPLETE;
  	}

@@ -551,7 +552,7 @@ bool nvme_cancel_request(struct request *req, void 
*data)
  	if (blk_mq_rq_state(req) != MQ_RQ_IN_FLIGHT)
  		return true;

-	nvme_req(req)->status = NVME_SC_HOST_ABORTED_CMD;
+	nvme_req(req)->status = NVME_SC_HOST_ABORTED_CMD | NVME_STATUS_DNR;
  	nvme_req(req)->flags |= NVME_REQ_CANCELLED;
  	blk_mq_complete_request(req);
  	return true;

Bart.