linux-kernel - [PATCH -next 1/2] md: factor out helpers to grab and put 'active

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Message-Id: <20230830092902.1236950-2-yukuai1@huaweicloud.com>
Date:   Wed, 30 Aug 2023 17:29:01 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     song@...nel.org, xni@...hat.com
Cc:     linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        yukuai3@...wei.com, yukuai1@...weicloud.com, yi.zhang@...wei.com,
        yangerkun@...wei.com
Subject: [PATCH -next 1/2] md: factor out helpers to grab and put 'active_io'

From: Yu Kuai <yukuai3@...wei.com>

There are no functional changes, prepare to fix a problem that 'sb_wait'
is not woke up while 'active_io' is decreased to 0.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 drivers/md/md.c | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 0fe7ab6e8ab9..0d69b1a2e2d5 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -368,16 +368,18 @@ static bool is_suspended(struct mddev *mddev, struct bio *bio)
 	return true;
 }
 
-void md_handle_request(struct mddev *mddev, struct bio *bio)
+static bool md_array_enter(struct mddev *mddev, struct bio *bio)
 {
 check_suspended:
 	if (is_suspended(mddev, bio)) {
 		DEFINE_WAIT(__wait);
+
 		/* Bail out if REQ_NOWAIT is set for the bio */
 		if (bio->bi_opf & REQ_NOWAIT) {
 			bio_wouldblock_error(bio);
-			return;
+			return false;
 		}
+
 		for (;;) {
 			prepare_to_wait(&mddev->sb_wait, &__wait,
 					TASK_UNINTERRUPTIBLE);
@@ -387,15 +389,34 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
 		}
 		finish_wait(&mddev->sb_wait, &__wait);
 	}
+
 	if (!percpu_ref_tryget_live(&mddev->active_io))
 		goto check_suspended;
 
+	return true;
+}
+
+static void md_array_exit(struct mddev *mddev)
+{
+	percpu_ref_put(&mddev->active_io);
+}
+
+void md_handle_request(struct mddev *mddev, struct bio *bio)
+{
+retry:
+	if (!md_array_enter(mddev, bio))
+		return;
+
 	if (!mddev->pers->make_request(mddev, bio)) {
-		percpu_ref_put(&mddev->active_io);
-		goto check_suspended;
+		md_array_exit(mddev);
+		goto retry;
 	}
 
-	percpu_ref_put(&mddev->active_io);
+	/*
+	 * pers->make_request() will grab additional reference until bio is
+	 * done.
+	 */
+	md_array_exit(mddev);
 }
 EXPORT_SYMBOL(md_handle_request);
 
@@ -8667,7 +8688,7 @@ static void md_end_clone_io(struct bio *bio)
 
 	bio_put(bio);
 	bio_endio(orig_bio);
-	percpu_ref_put(&mddev->active_io);
+	md_array_exit(mddev);
 }
 
 static void md_clone_bio(struct mddev *mddev, struct bio **bio)
-- 
2.39.2