[moderation] [block?] KCSAN: data-race in blk_mq_dispatch_rq_list / blk_mq_dispatch_rq_list (10)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 416f99c3b16f Merge tag 'driver-core-6.19-rc1' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1479421a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=68e2aa566f4b916e
dashboard link: https://syzkaller.appspot.com/bug?extid=97cd95101437be893150
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/b795aefada57/disk-416f99c3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/642270208071/vmlinux-416f99c3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b4c32cc091b5/bzImage-416f99c3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+97cd95...@syzkaller.appspotmail.com

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

read-write to 0xffff8881008abaf8 of 4 bytes by task 24 on cpu 1:
blk_mq_update_dispatch_busy block/blk-mq.c:2016 [inline]
blk_mq_dispatch_rq_list+0xc76/0xf80 block/blk-mq.c:2225
__blk_mq_sched_dispatch_requests+0x1c8/0xc70 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:2375
blk_mq_run_hw_queues+0x18e/0x270 block/blk-mq.c:2424
blk_mq_requeue_work+0x3b9/0x3f0 block/blk-mq.c:1591
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340
worker_thread+0x582/0x770 kernel/workqueue.c:3421
kthread+0x489/0x510 kernel/kthread.c:463
ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffff8881008abaf8 of 4 bytes by task 48 on cpu 0:
blk_mq_update_dispatch_busy block/blk-mq.c:2006 [inline]
blk_mq_dispatch_rq_list+0x8d3/0xf80 block/blk-mq.c:2229
__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+0x7eb/0xc70 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0x86/0x120 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x66/0xe0 block/blk-mq.c:2551
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340
worker_thread+0x582/0x770 kernel/workqueue.c:3421
kthread+0x489/0x510 kernel/kthread.c:463
ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

value changed: 0x00000003 -> 0x00000004

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 48 Comm: kworker/0:1H Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: kblockd blk_mq_run_work_fn
==================================================================


---
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