btrfs: opencode trivial compressed_bio_alloc, simplify error handling

compressed_bio_alloc is now a trivial wrapper around btrfs_bio_alloc, no
point keeping it. The error handling can be simplified, as we know
btrfs_bio_alloc will never fail.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -54,12 +54,6 @@ static inline int compressed_bio_size(struct btrfs_fs_info *fs_info,
 		(DIV_ROUND_UP(disk_size, fs_info->sectorsize)) * csum_size;
 }
 
-static struct bio *compressed_bio_alloc(struct block_device *bdev,
-					u64 first_byte, gfp_t gfp_flags)
-{
-	return btrfs_bio_alloc(bdev, first_byte >> 9);
-}
-
 static int check_compressed_csum(struct btrfs_inode *inode,
 				 struct compressed_bio *cb,
 				 u64 disk_start)
@@ -312,11 +306,7 @@ int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 
 	bdev = fs_info->fs_devices->latest_bdev;
 
-	bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
-	if (!bio) {
-		kfree(cb);
-		return -ENOMEM;
-	}
+	bio = btrfs_bio_alloc(bdev, first_byte >> 9);
 	bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
 	bio->bi_private = cb;
 	bio->bi_end_io = end_compressed_bio_write;
@@ -363,8 +353,7 @@ int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 
 			bio_put(bio);
 
-			bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
-			BUG_ON(!bio);
+			bio = btrfs_bio_alloc(bdev, first_byte >> 9);
 			bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
 			bio->bi_private = cb;
 			bio->bi_end_io = end_compressed_bio_write;
@@ -607,9 +596,7 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	/* include any pages we added in add_ra-bio_pages */
 	cb->len = bio->bi_iter.bi_size;
 
-	comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS);
-	if (!comp_bio)
-		goto fail2;
+	comp_bio = btrfs_bio_alloc(bdev, cur_disk_byte >> 9);
 	bio_set_op_attrs (comp_bio, REQ_OP_READ, 0);
 	comp_bio->bi_private = cb;
 	comp_bio->bi_end_io = end_compressed_bio_read;
@@ -660,9 +647,7 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 
 			bio_put(comp_bio);
 
-			comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
-							GFP_NOFS);
-			BUG_ON(!comp_bio);
+			comp_bio = btrfs_bio_alloc(bdev, cur_disk_byte >> 9);
 			bio_set_op_attrs(comp_bio, REQ_OP_READ, 0);
 			comp_bio->bi_private = cb;
 			comp_bio->bi_end_io = end_compressed_bio_read;