[moderation] [block?] KCSAN: data-race in lo_ioctl / loop_queue_rq (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 72761a7e3122 Merge tag 'driver-core-6.18-rc3' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15512258580000
kernel config: https://syzkaller.appspot.com/x/.config?x=15383e23338541bf
dashboard link: https://syzkaller.appspot.com/bug?extid=9e4925574d12b732f6a0
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/ab21b32e3385/disk-72761a7e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c1dde9668b38/vmlinux-72761a7e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2d9a7a942e42/bzImage-72761a7e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9e4925...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in lo_ioctl / loop_queue_rq

write to 0xffff8881023cdc80 of 4 bytes by task 11028 on cpu 0:
loop_clr_fd drivers/block/loop.c:1222 [inline]
lo_ioctl+0xa66/0x12b0 drivers/block/loop.c:1549
blkdev_ioctl+0x356/0x440 block/ioctl.c:705
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+0x1816/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881023cdc80 of 4 bytes by task 24 on cpu 1:
loop_queue_rq+0x4f/0x680 drivers/block/loop.c:1862
blk_mq_dispatch_rq_list+0x2a6/0xf80 block/blk-mq.c:2129
__blk_mq_sched_dispatch_requests+0xb83/0xc60 block/blk-mq-sched.c:313
blk_mq_sched_dispatch_requests+0x86/0x120 block/blk-mq-sched.c:329
blk_mq_run_hw_queue+0x17e/0x220 block/blk-mq.c:2367
blk_mq_run_hw_queues+0x180/0x250 block/blk-mq.c:2416
blk_mq_requeue_work+0x3b9/0x3f0 block/blk-mq.c:1583
process_one_work kernel/workqueue.c:3263 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3346
worker_thread+0x582/0x770 kernel/workqueue.c:3427
kthread+0x489/0x510 kernel/kthread.c:463
ret_from_fork+0x122/0x1b0 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00000001 -> 0x00000002

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 24 Comm: kworker/1:0H Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: kblockd blk_mq_requeue_work
==================================================================


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