Re: [PATCH 4/7] md/raid10: raid10_write_request() drops the barrier before calling

Hi,

在 2026/6/23 15:24, Abd-Alrhman Masalkhi 写道:
> bio_submit_split_bioset() and reacquires it afterwards. This is
> unnecessary because bio_submit_split_bioset() does not require
> releasing the barrier protection.

Why is this safe?

It's possible plug is not enabled in this context, and the allocated new
aplit bio will be submitted and enter wait_barrier() again. wait_barrier()
is not supposed to be called recursively. Otherwise deadlock can happend:

t1: sync_thread grab barrier and waiting for nr_pending to be 0 from raise_barrier()
t2: wait_barrier() first inc nr_pending, then recursive wait_barrier() waiting
for barrier to be released.

>
> Remove the redundant allow_barrier()/wait_barrier() pair around
> bio_submit_split_bioset().
>
> Signed-off-by: Abd-Alrhman Masalkhi <[email protected]>
> ---
>   drivers/md/raid10.c | 2 --
>   1 file changed, 2 deletions(-)
>
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 840f0446c231..4bc1d5553ec7 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -1493,10 +1493,8 @@ static bool raid10_write_request(struct mddev *mddev, struct bio *bio,
>   		if (atomic)
>   			goto err_handle;
>   
> -		allow_barrier(conf);
>   		bio = bio_submit_split_bioset(bio, r10_bio->sectors,
>   					      &conf->bio_split);
> -		wait_barrier(conf, false);
>   		if (!bio) {
>   			set_bit(R10BIO_Returned, &r10_bio->state);
>   			goto err_handle;

-- 
Thanks,
Kuai