btrfs: convert btrfs_dio_private->pending_bios to refcount_t

This is really a reference count now, so convert it to refcount_t and
rename it to refs.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/btrfs_inode.h

@@ -7,6 +7,7 @@
 #define BTRFS_INODE_H
 
 #include <linux/hash.h>
+#include <linux/refcount.h>
 #include "extent_map.h"
 #include "extent_io.h"
 #include "ordered-data.h"
@@ -302,8 +303,11 @@ struct btrfs_dio_private {
 	u64 disk_bytenr;
 	u64 bytes;
 
-	/* number of bios pending for this dio */
-	atomic_t pending_bios;
+	/*
+	 * References to this structure. There is one reference per in-flight
+	 * bio plus one while we're still setting up.
+	 */
+	refcount_t refs;
 
 	/* IO errors */
 	int errors;

fs/btrfs/inode.c

@@ -7811,7 +7811,7 @@ static void btrfs_end_dio_bio(struct bio *bio)
 	}
 
 	/* if there are more bios still pending for this dio, just exit */
-	if (!atomic_dec_and_test(&dip->pending_bios))
+	if (!refcount_dec_and_test(&dip->refs))
 		goto out;
 
 	if (dip->errors) {
@@ -7929,7 +7929,7 @@ static struct btrfs_dio_private *btrfs_create_dio_private(struct bio *dio_bio,
 	dip->disk_bytenr = (u64)dio_bio->bi_iter.bi_sector << 9;
 	dip->orig_bio = bio;
 	dip->dio_bio = dio_bio;
-	atomic_set(&dip->pending_bios, 1);
+	refcount_set(&dip->refs, 1);
 
 	if (write) {
 		struct btrfs_dio_data *dio_data = current->journal_info;
@@ -8025,13 +8025,13 @@ static void btrfs_submit_direct(struct bio *dio_bio, struct inode *inode,
 		 * count. Otherwise, the dip might get freed before we're
 		 * done setting it up.
 		 */
-		atomic_inc(&dip->pending_bios);
+		refcount_inc(&dip->refs);
 
 		status = btrfs_submit_dio_bio(bio, inode, file_offset,
 						async_submit);
 		if (status) {
 			bio_put(bio);
-			atomic_dec(&dip->pending_bios);
+			refcount_dec(&dip->refs);
 			goto out_err;
 		}
 
@@ -8060,7 +8060,7 @@ static void btrfs_submit_direct(struct bio *dio_bio, struct inode *inode,
 	 * atomic operations with a return value are fully ordered as per
 	 * atomic_t.txt
 	 */
-	if (atomic_dec_and_test(&dip->pending_bios))
+	if (refcount_dec_and_test(&dip->refs))
 		bio_io_error(dip->orig_bio);
 }