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From: Yu Kuai <yukuai1@huaweicloud.com>
To: czhong@redhat.com,
	xni@redhat.com,
	axboe@kernel.dk,
	yukuai3@huawei.com
Cc: linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	yukuai1@huaweicloud.com,
	yi.zhang@huawei.com,
	yangerkun@huawei.com
Subject: [PATCH -next] block: fix bio lost for plug enabeld bio based device
Date: Wed, 22 May 2024 04:03:08 +0800
Message-Id: <20240521200308.983986-1-yukuai1@huaweicloud.com>
In-Reply-To: <CAGVVp+UZ4stcktsHw0r8ks8LCfXvYJyT+zv93wEfGuuLswArnw@mail.gmail.com>
References: <CAGVVp+UZ4stcktsHw0r8ks8LCfXvYJyT+zv93wEfGuuLswArnw@mail.gmail.com>
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From: Yu Kuai <yukuai3@huawei.com>

With the following two conditions, bio will be lost:

1) blk plug is not enabled, for example, __blkdev_direct_IO_simple() and
__blkdev_direct_IO_async();
2) bio plug is enabled, for example write IO for raid1/raid10 while
bitmap is enabled;

Root cause is that blk_finish_plug() will add the bio to
curent->bio_list, while such bio will not be handled:

__submit_bio_noacct
 current->bio_list = bio_list_on_stack;
 blk_start_plug

 do {
  dm_submit_bio
   md_handle_request
    raid10_write_request
     -> generate new bio for underlying disks
     raid1_add_bio_to_plug -> bio is added to plug
 } while ((bio = bio_list_pop(&bio_list_on_stack[0])))
 -> previous bio are all handled

 blk_finish_plug
  raid10_unplug
   raid1_submit_write
    submit_bio_noacct
     if (current->bio_list)
      bio_list_add(&current->bio_list[0], bio)
      -> add new bio

 current->bio_list = NULL
 -> new bio is lost

Fix the problem by moving plug into the while loop, so that
current->bio_list will still be handled after blk_finish_plug().

By the way, enable plug for raid1/raid10 in this case will also prevent
delay IO handling into daemon thread, which should also improve IO
performance.

Fixes: 060406c61c7c ("block: add plug while submitting IO")
Reported-by: Changhui Zhong <czhong@redhat.com>
Closes: https://lore.kernel.org/all/CAGVVp+Xsmzy2G9YuEatfMT6qv1M--YdOCQ0g7z7OVmcTbBxQAg@mail.gmail.com/
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-core.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 01186333c88e..dd29d5465af6 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -613,9 +613,14 @@ static inline blk_status_t blk_check_zone_append(struct request_queue *q,
 
 static void __submit_bio(struct bio *bio)
 {
+	/* If plug is not used, add new plug here to cache nsecs time. */
+	struct blk_plug plug;
+
 	if (unlikely(!blk_crypto_bio_prep(&bio)))
 		return;
 
+	blk_start_plug(&plug);
+
 	if (!bio->bi_bdev->bd_has_submit_bio) {
 		blk_mq_submit_bio(bio);
 	} else if (likely(bio_queue_enter(bio) == 0)) {
@@ -624,6 +629,8 @@ static void __submit_bio(struct bio *bio)
 		disk->fops->submit_bio(bio);
 		blk_queue_exit(disk->queue);
 	}
+
+	blk_finish_plug(&plug);
 }
 
 /*
@@ -648,13 +655,11 @@ static void __submit_bio(struct bio *bio)
 static void __submit_bio_noacct(struct bio *bio)
 {
 	struct bio_list bio_list_on_stack[2];
-	struct blk_plug plug;
 
 	BUG_ON(bio->bi_next);
 
 	bio_list_init(&bio_list_on_stack[0]);
 	current->bio_list = bio_list_on_stack;
-	blk_start_plug(&plug);
 
 	do {
 		struct request_queue *q = bdev_get_queue(bio->bi_bdev);
@@ -688,23 +693,19 @@ static void __submit_bio_noacct(struct bio *bio)
 		bio_list_merge(&bio_list_on_stack[0], &bio_list_on_stack[1]);
 	} while ((bio = bio_list_pop(&bio_list_on_stack[0])));
 
-	blk_finish_plug(&plug);
 	current->bio_list = NULL;
 }
 
 static void __submit_bio_noacct_mq(struct bio *bio)
 {
 	struct bio_list bio_list[2] = { };
-	struct blk_plug plug;
 
 	current->bio_list = bio_list;
-	blk_start_plug(&plug);
 
 	do {
 		__submit_bio(bio);
 	} while ((bio = bio_list_pop(&bio_list[0])));
 
-	blk_finish_plug(&plug);
 	current->bio_list = NULL;
 }
 
-- 
2.39.2