[PATCH v2] btrfs: extract the parity scrub code into a helper

[Qu Wenruo <wqu@suse.com>]

The function scrub_raid56_parity_stripe() is handling the partity stripe
by the following steps:

- Scrub each data stripes
  And make sure everything is fine in each data stripe

- Cache the data stripe into the raid bio

- Use the cached raid bio to scrub the target parity stripe

Extract the last two steps into a new helper,
scrub_radi56_cached_parity(), as a cleanup and make the error handling
more straightforward.

With the following minor cleanups:

- Use on-stack bio structure
  The bio is always empty thus we do not need any bio vector nor the
  block device. Thus there is no need to allocate a bio, the on-stack
  one is more than enough to cut it.

- Remove the unnecessary btrfs_put_bioc() call if btrfs_map_block()
  failed
  If btrfs_map_block() is failed, @bioc_ret will not be touched thus
  there is no need to call btrfs_put_bioc() in this case.

- Use a proper out: tag to do the cleanup
  Now the error cleanup is much shorter and simpler, just
  btrfs_bio_counter_dec() and bio_uninit().

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Changelog:
v2:
- Rebased to the latest for-next branch
  The latest branch has the memory leak fixed merged, causing a minor
  conflict.

- Remove the DECLARE_COMPLETION_ONSTACK() inside the caller
  Which is no longer utilized.
---
 fs/btrfs/scrub.c | 93 +++++++++++++++++++++++++++---------------------
 1 file changed, 52 insertions(+), 41 deletions(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index b6278406a103..726e0c5ed4f2 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -2113,24 +2113,69 @@ static int should_cancel_scrub(const struct scrub_ctx *sctx)
 	return 0;
 }
 
+static int scrub_raid56_cached_parity(struct scrub_ctx *sctx,
+				      struct btrfs_device *scrub_dev,
+				      struct btrfs_chunk_map *map,
+				      u64 full_stripe_start,
+				      unsigned long *extent_bitmap)
+{
+	DECLARE_COMPLETION_ONSTACK(io_done);
+	struct btrfs_fs_info *fs_info = sctx->fs_info;
+	struct btrfs_io_context *bioc = NULL;
+	struct btrfs_raid_bio *rbio;
+	struct bio bio;
+	const int data_stripes = nr_data_stripes(map);
+	u64 length = btrfs_stripe_nr_to_offset(data_stripes);
+	int ret;
+
+	bio_init(&bio, NULL, NULL, 0, REQ_OP_READ);
+	bio.bi_iter.bi_sector = full_stripe_start >> SECTOR_SHIFT;
+	bio.bi_private = &io_done;
+	bio.bi_end_io = raid56_scrub_wait_endio;
+
+	btrfs_bio_counter_inc_blocked(fs_info);
+	ret = btrfs_map_block(fs_info, BTRFS_MAP_WRITE, full_stripe_start,
+			      &length, &bioc, NULL, NULL);
+	if (ret < 0)
+		goto out;
+	/* For RAID56 write there must be an @bioc allocated. */
+	ASSERT(bioc);
+	rbio = raid56_parity_alloc_scrub_rbio(&bio, bioc, scrub_dev, extent_bitmap,
+				BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits);
+	btrfs_put_bioc(bioc);
+	if (!rbio) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	/* Use the recovered stripes as cache to avoid read them from disk again. */
+	for (int i = 0; i < data_stripes; i++) {
+		struct scrub_stripe *stripe = &sctx->raid56_data_stripes[i];
+
+		raid56_parity_cache_data_folios(rbio, stripe->folios,
+				full_stripe_start + (i << BTRFS_STRIPE_LEN_SHIFT));
+	}
+	raid56_parity_submit_scrub_rbio(rbio);
+	wait_for_completion_io(&io_done);
+	ret = blk_status_to_errno(bio.bi_status);
+out:
+	btrfs_bio_counter_dec(fs_info);
+	bio_uninit(&bio);
+	return ret;
+}
+
 static int scrub_raid56_parity_stripe(struct scrub_ctx *sctx,
 				      struct btrfs_device *scrub_dev,
 				      struct btrfs_block_group *bg,
 				      struct btrfs_chunk_map *map,
 				      u64 full_stripe_start)
 {
-	DECLARE_COMPLETION_ONSTACK(io_done);
 	struct btrfs_fs_info *fs_info = sctx->fs_info;
-	struct btrfs_raid_bio *rbio;
-	struct btrfs_io_context *bioc = NULL;
 	struct btrfs_path extent_path = { 0 };
 	struct btrfs_path csum_path = { 0 };
-	struct bio *bio;
 	struct scrub_stripe *stripe;
 	bool all_empty = true;
 	const int data_stripes = nr_data_stripes(map);
 	unsigned long extent_bitmap = 0;
-	u64 length = btrfs_stripe_nr_to_offset(data_stripes);
 	int ret;
 
 	ASSERT(sctx->raid56_data_stripes);
@@ -2252,42 +2297,8 @@ static int scrub_raid56_parity_stripe(struct scrub_ctx *sctx,
 	}
 
 	/* Now we can check and regenerate the P/Q stripe. */
-	bio = bio_alloc(NULL, 1, REQ_OP_READ, GFP_NOFS);
-	bio->bi_iter.bi_sector = full_stripe_start >> SECTOR_SHIFT;
-	bio->bi_private = &io_done;
-	bio->bi_end_io = raid56_scrub_wait_endio;
-
-	btrfs_bio_counter_inc_blocked(fs_info);
-	ret = btrfs_map_block(fs_info, BTRFS_MAP_WRITE, full_stripe_start,
-			      &length, &bioc, NULL, NULL);
-	if (ret < 0) {
-		bio_put(bio);
-		btrfs_put_bioc(bioc);
-		btrfs_bio_counter_dec(fs_info);
-		goto out;
-	}
-	rbio = raid56_parity_alloc_scrub_rbio(bio, bioc, scrub_dev, &extent_bitmap,
-				BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits);
-	btrfs_put_bioc(bioc);
-	if (!rbio) {
-		ret = -ENOMEM;
-		bio_put(bio);
-		btrfs_bio_counter_dec(fs_info);
-		goto out;
-	}
-	/* Use the recovered stripes as cache to avoid read them from disk again. */
-	for (int i = 0; i < data_stripes; i++) {
-		stripe = &sctx->raid56_data_stripes[i];
-
-		raid56_parity_cache_data_folios(rbio, stripe->folios,
-				full_stripe_start + (i << BTRFS_STRIPE_LEN_SHIFT));
-	}
-	raid56_parity_submit_scrub_rbio(rbio);
-	wait_for_completion_io(&io_done);
-	ret = blk_status_to_errno(bio->bi_status);
-	bio_put(bio);
-	btrfs_bio_counter_dec(fs_info);
-
+	ret = scrub_raid56_cached_parity(sctx, scrub_dev, map, full_stripe_start,
+					 &extent_bitmap);
 out:
 	btrfs_release_path(&extent_path);
 	btrfs_release_path(&csum_path);
-- 
2.51.2