btrfs: add an ordered_extent pointer to struct btrfs_bio

Add a pointer to the ordered_extent to the existing union in struct
btrfs_bio, so all code dealing with data write bios can just use a
pointer dereference to retrieve the ordered_extent instead of doing
multiple rbtree lookups per I/O.

The reference to this ordered_extent is dropped at end I/O time,
which implies that an extra one must be acquired when the bio is split.
This also requires moving the btrfs_extract_ordered_extent call into
btrfs_split_bio so that the invariant of always having a valid
ordered_extent reference for the btrfs_bio is kept.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/bio.c

@@ -33,6 +33,11 @@ static inline bool is_data_bbio(struct btrfs_bio *bbio)
 	return bbio->inode && is_data_inode(&bbio->inode->vfs_inode);
 }
 
+static bool bbio_has_ordered_extent(struct btrfs_bio *bbio)
+{
+	return is_data_bbio(bbio) && btrfs_op(&bbio->bio) == BTRFS_MAP_WRITE;
+}
+
 /*
  * Initialize a btrfs_bio structure.  This skips the embedded bio itself as it
  * is already initialized by the block layer.
@@ -88,11 +93,40 @@ static struct btrfs_bio *btrfs_split_bio(struct btrfs_fs_info *fs_info,
 	bbio->inode = orig_bbio->inode;
 	bbio->file_offset = orig_bbio->file_offset;
 	orig_bbio->file_offset += map_length;
-
+	if (bbio_has_ordered_extent(bbio)) {
+		refcount_inc(&orig_bbio->ordered->refs);
+		bbio->ordered = orig_bbio->ordered;
+	}
 	atomic_inc(&orig_bbio->pending_ios);
 	return bbio;
 }
 
+/* Free a bio that was never submitted to the underlying device. */
+static void btrfs_cleanup_bio(struct btrfs_bio *bbio)
+{
+	if (bbio_has_ordered_extent(bbio))
+		btrfs_put_ordered_extent(bbio->ordered);
+	bio_put(&bbio->bio);
+}
+
+static void __btrfs_bio_end_io(struct btrfs_bio *bbio)
+{
+	if (bbio_has_ordered_extent(bbio)) {
+		struct btrfs_ordered_extent *ordered = bbio->ordered;
+
+		bbio->end_io(bbio);
+		btrfs_put_ordered_extent(ordered);
+	} else {
+		bbio->end_io(bbio);
+	}
+}
+
+void btrfs_bio_end_io(struct btrfs_bio *bbio, blk_status_t status)
+{
+	bbio->bio.bi_status = status;
+	__btrfs_bio_end_io(bbio);
+}
+
 static void btrfs_orig_write_end_io(struct bio *bio);
 
 static void btrfs_bbio_propagate_error(struct btrfs_bio *bbio,
@@ -121,12 +155,12 @@ static void btrfs_orig_bbio_end_io(struct btrfs_bio *bbio)
 
 		if (bbio->bio.bi_status)
 			btrfs_bbio_propagate_error(bbio, orig_bbio);
-		bio_put(&bbio->bio);
+		btrfs_cleanup_bio(bbio);
 		bbio = orig_bbio;
 	}
 
 	if (atomic_dec_and_test(&bbio->pending_ios))
-		bbio->end_io(bbio);
+		__btrfs_bio_end_io(bbio);
 }
 
 static int next_repair_mirror(struct btrfs_failed_bio *fbio, int cur_mirror)
@@ -684,7 +718,7 @@ done:
 
 fail_put_bio:
 	if (map_length < length)
-		bio_put(bio);
+		btrfs_cleanup_bio(bbio);
 fail:
 	btrfs_bio_counter_dec(fs_info);
 	btrfs_bio_end_io(orig_bbio, ret);

fs/btrfs/bio.h

@@ -50,11 +50,13 @@ struct btrfs_bio {
 
 		/*
 		 * For data writes:
+		 * - ordered extent covering the bio
 		 * - pointer to the checksums for this bio
 		 * - original physical address from the allocator
 		 *   (for zone append only)
 		 */
 		struct {
+			struct btrfs_ordered_extent *ordered;
 			struct btrfs_ordered_sum *sums;
 			u64 orig_physical;
 		};
@@ -95,12 +97,7 @@ void btrfs_bio_init(struct btrfs_bio *bbio, struct btrfs_fs_info *fs_info,
 struct btrfs_bio *btrfs_bio_alloc(unsigned int nr_vecs, blk_opf_t opf,
 				  struct btrfs_fs_info *fs_info,
 				  btrfs_bio_end_io_t end_io, void *private);
-
-static inline void btrfs_bio_end_io(struct btrfs_bio *bbio, blk_status_t status)
-{
-	bbio->bio.bi_status = status;
-	bbio->end_io(bbio);
-}
+void btrfs_bio_end_io(struct btrfs_bio *bbio, blk_status_t status);
 
 /* Submit using blkcg_punt_bio_submit. */
 #define REQ_BTRFS_CGROUP_PUNT			REQ_FS_PRIVATE

fs/btrfs/compression.c

@@ -303,10 +303,10 @@ void btrfs_submit_compressed_write(struct btrfs_ordered_extent *ordered,
 	INIT_WORK(&cb->write_end_work, btrfs_finish_compressed_write_work);
 	cb->nr_pages = nr_pages;
 	cb->bbio.bio.bi_iter.bi_sector = ordered->disk_bytenr >> SECTOR_SHIFT;
+	cb->bbio.ordered = ordered;
 	btrfs_add_compressed_bio_pages(cb);
 
 	btrfs_submit_bio(&cb->bbio, 0);
-	btrfs_put_ordered_extent(ordered);
 }
 
 /*

fs/btrfs/extent_io.c

@@ -835,7 +835,7 @@ static void alloc_new_bio(struct btrfs_inode *inode,
 			bio_ctrl->len_to_oe_boundary = min_t(u32, U32_MAX,
 					ordered->file_offset +
 					ordered->disk_num_bytes - file_offset);
-			btrfs_put_ordered_extent(ordered);
+			bbio->ordered = ordered;
 		}
 
 		/*

fs/btrfs/file-item.c

@@ -799,19 +799,12 @@ blk_status_t btrfs_csum_one_bio(struct btrfs_bio *bbio)
  */
 blk_status_t btrfs_alloc_dummy_sum(struct btrfs_bio *bbio)
 {
-	struct btrfs_ordered_extent *ordered =
-		btrfs_lookup_ordered_extent(bbio->inode, bbio->file_offset);
-
-	if (WARN_ON_ONCE(!ordered))
-		return BLK_STS_IOERR;
-
 	bbio->sums = kmalloc(sizeof(*bbio->sums), GFP_NOFS);
 	if (!bbio->sums)
 		return BLK_STS_RESOURCE;
 	bbio->sums->len = bbio->bio.bi_iter.bi_size;
 	bbio->sums->logical = bbio->bio.bi_iter.bi_sector << SECTOR_SHIFT;
-	btrfs_add_ordered_sum(ordered, bbio->sums);
-	btrfs_put_ordered_extent(ordered);
+	btrfs_add_ordered_sum(bbio->ordered, bbio->sums);
 	return 0;
 }
 

fs/btrfs/inode.c

@@ -2716,8 +2716,11 @@ static int btrfs_extract_ordered_extent(struct btrfs_bio *bbio,
 		return -EINVAL;
 
 	/* No need to split if the ordered extent covers the entire bio. */
-	if (ordered->disk_num_bytes == len)
+	if (ordered->disk_num_bytes == len) {
+		refcount_inc(&ordered->refs);
+		bbio->ordered = ordered;
 		return 0;
+	}
 
 	/*
 	 * Don't split the extent_map for NOCOW extents, as we're writing into
@@ -2734,8 +2737,7 @@ static int btrfs_extract_ordered_extent(struct btrfs_bio *bbio,
 	new = btrfs_split_ordered_extent(ordered, len);
 	if (IS_ERR(new))
 		return PTR_ERR(new);
-	btrfs_put_ordered_extent(new);
-
+	bbio->ordered = new;
 	return 0;
 }