linux-kernel - Re: [PATCH v2 06/12] md/raid5: Drop the do_prepare flag in raid5_make

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Date:   Wed, 27 Apr 2022 10:11:36 +0800
From:   Guoqing Jiang <guoqing.jiang@...ux.dev>
To:     Logan Gunthorpe <logang@...tatee.com>,
        linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
        Song Liu <song@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Stephen Bates <sbates@...thlin.com>,
        Martin Oliveira <Martin.Oliveira@...eticom.com>,
        David Sloan <David.Sloan@...eticom.com>
Subject: Re: [PATCH v2 06/12] md/raid5: Drop the do_prepare flag in
 raid5_make_request()



On 4/21/22 3:54 AM, Logan Gunthorpe wrote:
> prepare_to_wait() can be reasonably called after schedule instead of
> setting a flag and preparing in the next loop iteration.
>
> This means that prepare_to_wait() will be called before
> read_seqcount_begin(), but there shouldn't be any reason that
> the order matters here. On the first iteration of the loop
> prepare_to_wait() is already called first.
>
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> ---
>   drivers/md/raid5.c | 8 ++------
>   1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 5a7334ba0997..b9f618356446 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -5915,7 +5915,6 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
>   	const int rw = bio_data_dir(bi);
>   	enum stripe_result res;
>   	DEFINE_WAIT(w);
> -	bool do_prepare;
>   
>   	if (unlikely(bi->bi_opf & REQ_PREFLUSH)) {
>   		int ret = log_handle_flush_request(conf, bi);
> @@ -5973,12 +5972,8 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
>   	for (; logical_sector < last_sector; logical_sector += RAID5_STRIPE_SECTORS(conf)) {
>   		int seq;
>   
> -		do_prepare = false;
>   	retry:
>   		seq = read_seqcount_begin(&conf->gen_lock);
> -		if (do_prepare)
> -			prepare_to_wait(&conf->wait_for_overlap, &w,
> -				TASK_UNINTERRUPTIBLE);
>   
>   		res = make_stripe_request(mddev, conf, &ctx, logical_sector,
>   					  bi, seq);
> @@ -5988,7 +5983,8 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
>   			goto retry;
>   		} else if (res == STRIPE_SCHEDULE_AND_RETRY) {
>   			schedule();
> -			do_prepare = true;
> +			prepare_to_wait(&conf->wait_for_overlap, &w,
> +					TASK_UNINTERRUPTIBLE);
>   			goto retry;
>   		}
>   	}

Reviewed-by: Guoqing Jiang <guoqing.jiang@...ux.dev>

Thanks,
Guoqing