1 files changed, 41 insertions, 6 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a8ff25aedca1..a22b5cc921ad 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4815,14 +4815,49 @@ out_fail:
          * If the inodes csum_bytes is the same as the original
          * csum_bytes then we know we haven't raced with any free()ers
          * so we can just reduce our inodes csum bytes and carry on.
-         * Otherwise we have to do the normal free thing to account for
-         * the case that the free side didn't free up its reserve
-         * because of this outstanding reservation.
          */
-        if (BTRFS_I(inode)->csum_bytes == csum_bytes)
+        if (BTRFS_I(inode)->csum_bytes == csum_bytes) {
                 calc_csum_metadata_size(inode, num_bytes, 0);
-        else
-                to_free = calc_csum_metadata_size(inode, num_bytes, 0);
+        } else {
+                u64 orig_csum_bytes = BTRFS_I(inode)->csum_bytes;
+                u64 bytes;
+
+                /*
+                 * This is tricky, but first we need to figure out how much we
+                 * free'd from any free-ers that occured during this
+                 * reservation, so we reset ->csum_bytes to the csum_bytes
+                 * before we dropped our lock, and then call the free for the
+                 * number of bytes that were freed while we were trying our
+                 * reservation.
+                 */
+                bytes = csum_bytes - BTRFS_I(inode)->csum_bytes;
+                BTRFS_I(inode)->csum_bytes = csum_bytes;
+                to_free = calc_csum_metadata_size(inode, bytes, 0);
+
+
+                /*
+                 * Now we need to see how much we would have freed had we not
+                 * been making this reservation and our ->csum_bytes were not
+                 * artificially inflated.
+                 */
+                BTRFS_I(inode)->csum_bytes = csum_bytes - num_bytes;
+                bytes = csum_bytes - orig_csum_bytes;
+                bytes = calc_csum_metadata_size(inode, bytes, 0);
+
+                /*
+                 * Now reset ->csum_bytes to what it should be.  If bytes is
+                 * more than to_free then we would have free'd more space had we
+                 * not had an artificially high ->csum_bytes, so we need to free
+                 * the remainder.  If bytes is the same or less then we don't
+                 * need to do anything, the other free-ers did the correct
+                 * thing.
+                 */
+                BTRFS_I(inode)->csum_bytes = orig_csum_bytes - num_bytes;
+                if (bytes > to_free)
+                        to_free = bytes - to_free;
+                else
+                        to_free = 0;
+        }
         spin_unlock(&BTRFS_I(inode)->lock);
         if (dropped)
                 to_free += btrfs_calc_trans_metadata_size(root, dropped);