btrfs: use on-stack variable for block reserve in btrfs_truncate()

We can avoid potential memory allocation failure in btrfs_truncate() as
the block reserve lifetime is limited to the scope of the function. This
requires +48 bytes on stack.

Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 868c9dba16d4600f45709940a4618c6dcd234c80..317761f7c1c90b65e4eeeaa5cccae8dc8263516b 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7606,7 +7606,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
        };
        struct btrfs_root *root = inode->root;
        struct btrfs_fs_info *fs_info = root->fs_info;
-       struct btrfs_block_rsv *rsv;
+       struct btrfs_block_rsv rsv;
        int ret;
        struct btrfs_trans_handle *trans;
        u64 mask = fs_info->sectorsize - 1;
@@ -7648,11 +7648,9 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
         * 2) fs_info->trans_block_rsv - this will have 1 items worth left for
         * updating the inode.
         */
-       rsv = btrfs_alloc_block_rsv(fs_info, BTRFS_BLOCK_RSV_TEMP);
-       if (!rsv)
-               return -ENOMEM;
-       rsv->size = min_size;
-       rsv->failfast = true;
+       btrfs_init_metadata_block_rsv(fs_info, &rsv, BTRFS_BLOCK_RSV_TEMP);
+       rsv.size = min_size;
+       rsv.failfast = true;
 
        /*
         * 1 for the truncate slack space
@@ -7665,7 +7663,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
        }
 
        /* Migrate the slack space for the truncate to our reserve */
-       ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, rsv,
+       ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, &rsv,
                                      min_size, false);
        /*
         * We have reserved 2 metadata units when we started the transaction and
@@ -7677,7 +7675,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
                goto out;
        }
 
-       trans->block_rsv = rsv;
+       trans->block_rsv = &rsv;
 
        while (1) {
                struct extent_state *cached_state = NULL;
@@ -7720,9 +7718,9 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
                        break;
                }
 
-               btrfs_block_rsv_release(fs_info, rsv, -1, NULL);
+               btrfs_block_rsv_release(fs_info, &rsv, -1, NULL);
                ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv,
-                                             rsv, min_size, false);
+                                             &rsv, min_size, false);
                /*
                 * We have reserved 2 metadata units when we started the
                 * transaction and min_size matches 1 unit, so this should never
@@ -7731,7 +7729,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
                if (WARN_ON(ret))
                        break;
 
-               trans->block_rsv = rsv;
+               trans->block_rsv = &rsv;
        }
 
        /*
@@ -7770,7 +7768,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
                btrfs_btree_balance_dirty(fs_info);
        }
 out:
-       btrfs_free_block_rsv(fs_info, rsv);
+       btrfs_block_rsv_release(fs_info, &rsv, (u64)-1, NULL);
        /*
         * So if we truncate and then write and fsync we normally would just
         * write the extents that changed, which is a problem if we need to