1 files changed, 57 insertions, 1 deletions

diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 3a1b939c9ae2..5b163572e0ca 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -617,12 +617,14 @@ static void btrfs_delayed_item_release_metadata(struct btrfs_root *root,
 static int btrfs_delayed_inode_reserve_metadata(
                                         struct btrfs_trans_handle *trans,
                                         struct btrfs_root *root,
+                                        struct inode *inode,
                                         struct btrfs_delayed_node *node)
 {
         struct btrfs_block_rsv *src_rsv;
         struct btrfs_block_rsv *dst_rsv;
         u64 num_bytes;
         int ret;
+        int release = false;
 
         src_rsv = trans->block_rsv;
         dst_rsv = &root->fs_info->delayed_block_rsv;
@@ -652,12 +654,65 @@ static int btrfs_delayed_inode_reserve_metadata(
                 if (!ret)
                         node->bytes_reserved = num_bytes;
                 return ret;
+        } else if (src_rsv == &root->fs_info->delalloc_block_rsv) {
+                spin_lock(&BTRFS_I(inode)->lock);
+                if (BTRFS_I(inode)->delalloc_meta_reserved) {
+                        BTRFS_I(inode)->delalloc_meta_reserved = 0;
+                        spin_unlock(&BTRFS_I(inode)->lock);
+                        release = true;
+                        goto migrate;
+                }
+                spin_unlock(&BTRFS_I(inode)->lock);
+
+                /* Ok we didn't have space pre-reserved.  This shouldn't happen
+                 * too often but it can happen if we do delalloc to an existing
+                 * inode which gets dirtied because of the time update, and then
+                 * isn't touched again until after the transaction commits and
+                 * then we try to write out the data.  First try to be nice and
+                 * reserve something strictly for us.  If not be a pain and try
+                 * to steal from the delalloc block rsv.
+                 */
+                ret = btrfs_block_rsv_add_noflush(root, dst_rsv, num_bytes);
+                if (!ret)
+                        goto out;
+
+                ret = btrfs_block_rsv_migrate(src_rsv, dst_rsv, num_bytes);
+                if (!ret)
+                        goto out;
+
+                /*
+                 * Ok this is a problem, let's just steal from the global rsv
+                 * since this really shouldn't happen that often.
+                 */
+                WARN_ON(1);
+                ret = btrfs_block_rsv_migrate(&root->fs_info->global_block_rsv,
+                                              dst_rsv, num_bytes);
+                goto out;
         }
 
+migrate:
         ret = btrfs_block_rsv_migrate(src_rsv, dst_rsv, num_bytes);
+
+out:
+        /*
+         * Migrate only takes a reservation, it doesn't touch the size of the
+         * block_rsv.  This is to simplify people who don't normally have things
+         * migrated from their block rsv.  If they go to release their
+         * reservation, that will decrease the size as well, so if migrate
+         * reduced size we'd end up with a negative size.  But for the
+         * delalloc_meta_reserved stuff we will only know to drop 1 reservation,
+         * but we could in fact do this reserve/migrate dance several times
+         * between the time we did the original reservation and we'd clean it
+         * up.  So to take care of this, release the space for the meta
+         * reservation here.  I think it may be time for a documentation page on
+         * how block rsvs. work.
+         */
         if (!ret)
                 node->bytes_reserved = num_bytes;
 
+        if (release)
+                btrfs_block_rsv_release(root, src_rsv, num_bytes);
+
         return ret;
 }
 
@@ -1708,7 +1763,8 @@ int btrfs_delayed_update_inode(struct btrfs_trans_handle *trans,
                 goto release_node;
         }
 
-        ret = btrfs_delayed_inode_reserve_metadata(trans, root, delayed_node);
+        ret = btrfs_delayed_inode_reserve_metadata(trans, root, inode,
+                                                   delayed_node);
         if (ret)
                 goto release_node;