linux-kernel - [PATCH v3 07/15] md/raid5: Drop the do_prepare flag in raid5_make

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Date:   Thu, 16 Jun 2022 13:19:37 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
        Song Liu <song@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Guoqing Jiang <guoqing.jiang@...ux.dev>,
        Stephen Bates <sbates@...thlin.com>,
        Martin Oliveira <Martin.Oliveira@...eticom.com>,
        David Sloan <David.Sloan@...eticom.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Christoph Hellwig <hch@....de>
Subject: [PATCH v3 07/15] md/raid5: Drop the do_prepare flag in raid5_make_request()

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>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Guoqing Jiang <guoqing.jiang@...ux.dev>
---
 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 26ef292842de..c58e70db204a 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5918,7 +5918,6 @@ 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);
@@ -5976,12 +5975,8 @@ 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);
@@ -5993,7 +5988,8 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
 
 		if (res == STRIPE_SCHEDULE_AND_RETRY) {
 			schedule();
-			do_prepare = true;
+			prepare_to_wait(&conf->wait_for_overlap, &w,
+					TASK_UNINTERRUPTIBLE);
 			goto retry;
 		}
 	}
-- 
2.30.2