[RFC PATCH 2/2] ext4: undo ei->i_da_metadata_calc_len increment if we fail to claim space

[Brian Foster <bfoster@redhat.com>]

From: Brian Foster <bfoster@redhat.com>

If we call ext4_calc_metadata_amount() and then fail to claim
the space, a subsequent successful request to a block covered
by the same ext2 indirect block will set md_needed to 0, fail
to update the associated counters and result in a delayed md
block allocation without a reservation. Decrement
i_da_metadata_calc_len on failure to ensure the next
reservation sets md_needed correctly.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/ext4/inode.c |   18 ++++++++++++++++--
 1 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index b58845c..7d2a3c0 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1138,13 +1138,14 @@ repeat:
 	 * We do still charge estimated metadata to the sb though;
 	 * we cannot afford to run out of free blocks.
 	 */
-	if (ext4_claim_free_clusters(sbi, md_needed + 1, 0)) {
+	ret = ext4_claim_free_clusters(sbi, md_needed + 1, 0);
+	if (ret) {
 		dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1));
 		if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
 			yield();
 			goto repeat;
 		}
-		return -ENOSPC;
+		goto error;
 	}
 	spin_lock(&ei->i_block_reservation_lock);
 	ei->i_reserved_data_blocks++;
@@ -1152,6 +1153,19 @@ repeat:
 	spin_unlock(&ei->i_block_reservation_lock);
 
 	return 0;       /* success */
+
+error:
+	/*
+	 * We've failed to reserve the space. Undo the effect
+	 * of ext4_calc_metadata_amount() to ensure the next
+	 * attempt correctly accounts for metadata.
+	 */
+	spin_lock(&ei->i_block_reservation_lock);
+	if (ei->i_da_metadata_calc_len)
+		ei->i_da_metadata_calc_len--;
+	spin_unlock(&ei->i_block_reservation_lock);
+
+	return ret;
 }
 
 static void ext4_da_release_space(struct inode *inode, int to_free)
-- 
1.7.7.6