[moderation] [block?] KCSAN: data-race in blk_mq_dispatch_rq_list / blk_mq_dispatch_rq_list (11)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: bcc44b6785f2 Merge tag 'drm-fixes-2026-08-08' of https://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=138defb9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=33c5ac947f6be69e
dashboard link: https://syzkaller.appspot.com/bug?extid=62390798db3876edaafd
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
CC: [ax...@kernel.dk linux...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/86c05adcb9b2/disk-bcc44b67.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2c99bf1c591e/vmlinux-bcc44b67.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cb396a74db69/bzImage-bcc44b67.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+623907...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in blk_mq_dispatch_rq_list / blk_mq_dispatch_rq_list

read-write to 0xffff888102772af8 of 4 bytes by task 18706 on cpu 0:
blk_mq_update_dispatch_busy block/blk-mq.c:1996 [inline]
blk_mq_dispatch_rq_list+0xc3e/0xef0 block/blk-mq.c:2205
__blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
__blk_mq_sched_dispatch_requests+0x86c/0xce0 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0x86/0x120 block/blk-mq-sched.c:329
blk_mq_run_hw_queue+0x17e/0x220 block/blk-mq.c:2356
blk_mq_dispatch_list+0x83d/0x9f0 arch/x86/include/asm/bitops.h:-1
blk_mq_flush_plug_list+0x2cd/0x320 block/blk-mq.c:2966
blk_add_rq_to_plug+0xe4/0x360 block/blk-mq.c:1386
blk_mq_submit_bio+0xc11/0x1130 block/blk-mq.c:3198
__submit_bio+0x54/0x3d0 block/blk-core.c:673
__submit_bio_noacct_mq block/blk-core.c:756 [inline]
submit_bio_noacct_nocheck+0x1c6/0x620 block/blk-core.c:790
submit_bio_noacct+0x700/0x920 block/blk-core.c:921
submit_bio+0x2a4/0x2c0 block/blk-core.c:962
bio_chain_and_submit+0x84/0xb0 block/bio.c:376
__blkdev_issue_zero_pages+0x1f7/0x240 block/blk-lib.c:215
blkdev_issue_zero_pages block/blk-lib.c:231 [inline]
blkdev_issue_zeroout+0x3a1/0x4f0 block/blk-lib.c:312
blk_ioctl_zeroout block/ioctl.c:243 [inline]
blkdev_common_ioctl+0x1a07/0x2060 block/ioctl.c:666
blkdev_ioctl+0x31f/0x460 block/ioctl.c:791
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read-write to 0xffff888102772af8 of 4 bytes by task 2940 on cpu 1:
blk_mq_update_dispatch_busy block/blk-mq.c:1996 [inline]
blk_mq_dispatch_rq_list+0xc3e/0xef0 block/blk-mq.c:2205
__blk_mq_sched_dispatch_requests+0x1db/0xce0 block/blk-mq-sched.c:299
blk_mq_sched_dispatch_requests+0x86/0x120 block/blk-mq-sched.c:329
blk_mq_run_hw_queue+0x17e/0x220 block/blk-mq.c:2356
blk_mq_run_hw_queues+0x18e/0x270 block/blk-mq.c:2404
blk_mq_requeue_work+0x3ca/0x400 block/blk-mq.c:1571
process_one_work kernel/workqueue.c:3322 [inline]
process_scheduled_works+0x4d4/0x9a0 kernel/workqueue.c:3405
worker_thread+0x569/0x750 kernel/workqueue.c:3486
kthread+0x221/0x270 kernel/kthread.c:436
ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00000008 -> 0x00000009

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2940 Comm: kworker/1:1H Tainted: G W syzkaller #0 PREEMPT(lazy)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: kblockd blk_mq_requeue_work
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup