Btrfs: handle errors from btrfs_map_bio() everywhere

With the addition of the device replace procedure, it is possible
for btrfs_map_bio(READ) to report an error. This happens when the
specific mirror is requested which is located on the target disk,
and the copy operation has not yet copied this block. Hence the
block cannot be read and this error state is indicated by
returning EIO.
Some background information follows now. A new mirror is added
while the device replace procedure is running.
btrfs_get_num_copies() returns one more, and
btrfs_map_bio(GET_READ_MIRROR) adds one more mirror if a disk
location is involved that was already handled by the device
replace copy operation. The assigned mirror num is the highest
mirror number, e.g. the value 3 in case of RAID1.
If btrfs_map_bio() is invoked with mirror_num == 0 (i.e., select
any mirror), the copy on the target drive is never selected
because that disk shall be able to perform the write requests as
quickly as possible. The parallel execution of read requests would
only slow down the disk copy procedure. Second case is that
btrfs_map_bio() is called with mirror_num > 0. This is done from
the repair code only. In this case, the highest mirror num is
assigned to the target disk, since it is used last. And when this
mirror is not available because the copy procedure has not yet
handled this area, an error is returned. Everywhere in the code
the handling of such errors is added now.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 27 insertions, 17 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 9d1b7106081..0e410478ad2 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -852,11 +852,16 @@ static int __btree_submit_bio_done(struct inode *inode, int rw, struct bio *bio,
 				 int mirror_num, unsigned long bio_flags,
 				 u64 bio_offset)
 {
+	int ret;
+
 	/*
 	 * when we're called for a write, we're already in the async
 	 * submission context.  Just jump into btrfs_map_bio
 	 */
-	return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio, mirror_num, 1);
+	ret = btrfs_map_bio(BTRFS_I(inode)->root, rw, bio, mirror_num, 1);
+	if (ret)
+		bio_endio(bio, ret);
+	return ret;
 }
 
 static int check_async_write(struct inode *inode, unsigned long bio_flags)
@@ -878,7 +883,6 @@ static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
 	int ret;
 
 	if (!(rw & REQ_WRITE)) {
-
 		/*
 		 * called for a read, do the setup so that checksum validation
 		 * can happen in the async kernel threads
@@ -886,26 +890,32 @@ static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
 		ret = btrfs_bio_wq_end_io(BTRFS_I(inode)->root->fs_info,
 					  bio, 1);
 		if (ret)
-			return ret;
-		return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio,
-				     mirror_num, 0);
+			goto out_w_error;
+		ret = btrfs_map_bio(BTRFS_I(inode)->root, rw, bio,
+				    mirror_num, 0);
 	} else if (!async) {
 		ret = btree_csum_one_bio(bio);
 		if (ret)
-			return ret;
-		return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio,
-				     mirror_num, 0);
+			goto out_w_error;
+		ret = btrfs_map_bio(BTRFS_I(inode)->root, rw, bio,
+				    mirror_num, 0);
+	} else {
+		/*
+		 * kthread helpers are used to submit writes so that
+		 * checksumming can happen in parallel across all CPUs
+		 */
+		ret = btrfs_wq_submit_bio(BTRFS_I(inode)->root->fs_info,
+					  inode, rw, bio, mirror_num, 0,
+					  bio_offset,
+					  __btree_submit_bio_start,
+					  __btree_submit_bio_done);
 	}
 
-	/*
-	 * kthread helpers are used to submit writes so that checksumming
-	 * can happen in parallel across all CPUs
-	 */
-	return btrfs_wq_submit_bio(BTRFS_I(inode)->root->fs_info,
-				   inode, rw, bio, mirror_num, 0,
-				   bio_offset,
-				   __btree_submit_bio_start,
-				   __btree_submit_bio_done);
+	if (ret) {
+out_w_error:
+		bio_endio(bio, ret);
+	}
+	return ret;
 }
 
 #ifdef CONFIG_MIGRATION