Btrfs: always store the mirror we read the eb from

A user reported a panic where we were trying to fix a bad mirror but the
mirror number we were giving was 0, which is invalid.  This is because we
don't do the transid verification until after the read, so as far as the
read code is concerned the read was a success.  So instead store the mirror
we read from so that if there is some failure post read we know which mirror
to try next and which mirror needs to be fixed if we find a good copy of the
block.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 2a3ddd2..eff59fa 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -390,8 +390,7 @@
 
 		if (!failed_mirror) {
 			failed = 1;
-			printk(KERN_ERR "failed mirror was %d\n", eb->failed_mirror);
-			failed_mirror = eb->failed_mirror;
+			failed_mirror = eb->read_mirror;
 		}
 
 		mirror_num++;
@@ -564,7 +563,7 @@
 }
 
 static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
-			       struct extent_state *state)
+			       struct extent_state *state, int mirror)
 {
 	struct extent_io_tree *tree;
 	u64 found_start;
@@ -589,6 +588,7 @@
 	if (!reads_done)
 		goto err;
 
+	eb->read_mirror = mirror;
 	if (test_bit(EXTENT_BUFFER_IOERR, &eb->bflags)) {
 		ret = -EIO;
 		goto err;
@@ -652,7 +652,7 @@
 
 	eb = (struct extent_buffer *)page->private;
 	set_bit(EXTENT_BUFFER_IOERR, &eb->bflags);
-	eb->failed_mirror = failed_mirror;
+	eb->read_mirror = failed_mirror;
 	if (test_and_clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags))
 		btree_readahead_hook(root, eb, eb->start, -EIO);
 	return -EIO;	/* we fixed nothing */
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index cd4b5e4..a128a8c 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2301,7 +2301,7 @@
 	u64 start;
 	u64 end;
 	int whole_page;
-	int failed_mirror;
+	int mirror;
 	int ret;
 
 	if (err)
@@ -2340,20 +2340,18 @@
 		}
 		spin_unlock(&tree->lock);
 
+		mirror = (int)(unsigned long)bio->bi_bdev;
 		if (uptodate && tree->ops && tree->ops->readpage_end_io_hook) {
 			ret = tree->ops->readpage_end_io_hook(page, start, end,
-							      state);
+							      state, mirror);
 			if (ret)
 				uptodate = 0;
 			else
 				clean_io_failure(start, page);
 		}
 
-		if (!uptodate)
-			failed_mirror = (int)(unsigned long)bio->bi_bdev;
-
 		if (!uptodate && tree->ops && tree->ops->readpage_io_failed_hook) {
-			ret = tree->ops->readpage_io_failed_hook(page, failed_mirror);
+			ret = tree->ops->readpage_io_failed_hook(page, mirror);
 			if (!ret && !err &&
 			    test_bit(BIO_UPTODATE, &bio->bi_flags))
 				uptodate = 1;
@@ -2368,8 +2366,7 @@
 			 * can't handle the error it will return -EIO and we
 			 * remain responsible for that page.
 			 */
-			ret = bio_readpage_error(bio, page, start, end,
-							failed_mirror, NULL);
+			ret = bio_readpage_error(bio, page, start, end, mirror, NULL);
 			if (ret == 0) {
 				uptodate =
 					test_bit(BIO_UPTODATE, &bio->bi_flags);
@@ -4462,7 +4459,7 @@
 	}
 
 	clear_bit(EXTENT_BUFFER_IOERR, &eb->bflags);
-	eb->failed_mirror = 0;
+	eb->read_mirror = 0;
 	atomic_set(&eb->io_pages, num_reads);
 	for (i = start_i; i < num_pages; i++) {
 		page = extent_buffer_page(eb, i);
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index faf10eb..b516c3b 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -79,7 +79,7 @@
 					u64 start, u64 end,
 				       struct extent_state *state);
 	int (*readpage_end_io_hook)(struct page *page, u64 start, u64 end,
-				    struct extent_state *state);
+				    struct extent_state *state, int mirror);
 	int (*writepage_end_io_hook)(struct page *page, u64 start, u64 end,
 				      struct extent_state *state, int uptodate);
 	void (*set_bit_hook)(struct inode *inode, struct extent_state *state,
@@ -135,7 +135,7 @@
 	spinlock_t refs_lock;
 	atomic_t refs;
 	atomic_t io_pages;
-	int failed_mirror;
+	int read_mirror;
 	struct list_head leak_list;
 	struct rcu_head rcu_head;
 	pid_t lock_owner;
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 6b5f973..73808b8 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1947,7 +1947,7 @@
  * extent_io.c will try to find good copies for us.
  */
 static int btrfs_readpage_end_io_hook(struct page *page, u64 start, u64 end,
-			       struct extent_state *state)
+			       struct extent_state *state, int mirror)
 {
 	size_t offset = start - ((u64)page->index << PAGE_CACHE_SHIFT);
 	struct inode *inode = page->mapping->host;