[moderation] [block?] KCSAN: data-race in blk_mq_start_request / bt_for_each (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 20371ba12063 Merge tag 'drm-fixes-2024-08-30' of https://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12a11d39980000
kernel config: https://syzkaller.appspot.com/x/.config?x=6fafac02e339cc84
dashboard link: https://syzkaller.appspot.com/bug?extid=3912f6af732771b057ba
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
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/4a8763df1c20/disk-20371ba1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f9678a905383/vmlinux-20371ba1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ef6e49adc393/bzImage-20371ba1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3912f6...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in blk_mq_start_request / bt_for_each

write to 0xffff88810282d350 of 8 bytes by task 3369 on cpu 1:
blk_mq_start_request+0x1e4/0x3b0 block/blk-mq.c:1261
scsi_queue_rq+0x14aa/0x1a10 drivers/scsi/scsi_lib.c:1849
blk_mq_dispatch_rq_list+0x2a2/0xf30 block/blk-mq.c:2032
__blk_mq_do_dispatch_sched block/blk-mq-sched.c:170 [inline]
blk_mq_do_dispatch_sched block/blk-mq-sched.c:184 [inline]
__blk_mq_sched_dispatch_requests+0x604/0xd50 block/blk-mq-sched.c:309
blk_mq_sched_dispatch_requests+0x78/0xe0 block/blk-mq-sched.c:331
blk_mq_run_hw_queue+0x29c/0x4d0 block/blk-mq.c:2245
blk_mq_flush_plug_list+0x7bc/0xde0 block/blk-mq.c:2794
__blk_flush_plug+0x216/0x290 block/blk-core.c:1198
blk_finish_plug+0x48/0x70 block/blk-core.c:1225
wb_writeback+0x6d8/0x720 fs/fs-writeback.c:2165
wb_check_old_data_flush fs/fs-writeback.c:2233 [inline]
wb_do_writeback fs/fs-writeback.c:2286 [inline]
wb_workfn+0x615/0x940 fs/fs-writeback.c:2314
process_one_work kernel/workqueue.c:3231 [inline]
process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3312
worker_thread+0x526/0x6e0 kernel/workqueue.c:3389
kthread+0x1d1/0x210 kernel/kthread.c:389
ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

read to 0xffff88810282d350 of 8 bytes by task 392 on cpu 0:
blk_mq_find_and_get_req block/blk-mq-tag.c:260 [inline]
bt_iter block/blk-mq-tag.c:288 [inline]
__sbitmap_for_each_set include/linux/sbitmap.h:286 [inline]
sbitmap_for_each_set include/linux/sbitmap.h:307 [inline]
bt_for_each+0x279/0x480 block/blk-mq-tag.c:325
blk_mq_queue_tag_busy_iter+0x1a4/0x330 block/blk-mq-tag.c:534
blk_mq_timeout_work+0xc4/0x350 block/blk-mq.c:1639
process_one_work kernel/workqueue.c:3231 [inline]
process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3312
worker_thread+0x526/0x6e0 kernel/workqueue.c:3389
kthread+0x1d1/0x210 kernel/kthread.c:389
ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

value changed: 0xffff888102f08bc0 -> 0xffff888102f03dc0

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 392 Comm: kworker/0:1H Not tainted 6.11.0-rc5-syzkaller-00176-g20371ba12063 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
Workqueue: kblockd blk_mq_timeout_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