Re: [PATCH] md/raid5: fix lockless max_nr_stripes reads

[yu kuai]

在 2026/6/24 10:40, Chen Cheng 写道:

> From: Chen Cheng<chencheng@xxxxxxxxx>
>
> max_nr_stripes is updated under cache_size_mutex in the stripe cache
> grow/shrink paths, while is_inactive_blocked() and
> raid5_end_read_request() read it without that lock.
>
> Use READ_ONCE() for those reads in lockless path to match the WRITE_ONCE()
> updates and avoid KCSAN data race reports.
>
> A similar issue was previously fixed in commit-id:
> 	dfd2bf436709b2bccb78c2dda550dde93700efa7.
>
> Fixes: 0009fad033370 ("raid5 improve too many read errors msg by adding limits")
> Fixes: 3514da58be9c4 ("md/raid5: Make is_inactive_blocked() helper")
>
> KCSAN report:
> =================
>
> BUG: KCSAN: data-race in grow_one_stripe / is_inactive_blocked
>
> write (marked) to 0xffff8f01f0b5a268 of 4 bytes by task 12616 on cpu 9:
>   grow_one_stripe+0x2d8/0x320
>   raid5d+0xb57/0xba0
>   md_thread+0x15a/0x2d0
>   [..........]
>
> read to 0xffff8f01f0b5a268 of 4 bytes by task 12670 on cpu 11:
>   is_inactive_blocked+0x97/0xc0
>   raid5_get_active_stripe+0x2fd/0xa70
>   raid5_make_request+0x4aa/0x2940
>   [..........]
>
> value changed: 0x000003b9 -> 0x000003ba
>
> Signed-off-by: Chen Cheng<chencheng@xxxxxxxxx>
> ---
>   drivers/md/raid5.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
Reviewed-by: Yu Kuai <yukuai@xxxxxxx>

-- 
Thanks,
Kuai