Btrfs: only reserve space in fallocate if we have to do a preallocate

Lukas found a problem where if he tries to fallocate over the same region twice
and the first fallocate took up all the space we would fail with ENOSPC.  This
is because we reserve the total space we want to use for fallocate, regardless
of wether or not we will have to actually preallocate.  So instead move the
check into the loop where we actually have to do the preallocate.  Thanks,

Tested-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Josef Bacik <josef@redhat.com>
(cherry picked from commit 1b9c332b6c92e992b1971a08412c6f460a54b514)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index e730510993687962606e5f7a4e41f8fb79c1a0c5..d60f27c826f6f118213a000d8697fb0f4892c0bf 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1606,10 +1606,6 @@ static long btrfs_fallocate(struct file *file, int mode,
                        goto out;
        }
 
-       ret = btrfs_check_data_free_space(inode, alloc_end - alloc_start);
-       if (ret)
-               goto out;
-
        locked_end = alloc_end - 1;
        while (1) {
                struct btrfs_ordered_extent *ordered;
@@ -1655,11 +1651,27 @@ static long btrfs_fallocate(struct file *file, int mode,
                if (em->block_start == EXTENT_MAP_HOLE ||
                    (cur_offset >= inode->i_size &&
                     !test_bit(EXTENT_FLAG_PREALLOC, &em->flags))) {
+
+                       /*
+                        * Make sure we have enough space before we do the
+                        * allocation.
+                        */
+                       ret = btrfs_check_data_free_space(inode, last_byte -
+                                                         cur_offset);
+                       if (ret) {
+                               free_extent_map(em);
+                               break;
+                       }
+
                        ret = btrfs_prealloc_file_range(inode, mode, cur_offset,
                                                        last_byte - cur_offset,
                                                        1 << inode->i_blkbits,
                                                        offset + len,
                                                        &alloc_hint);
+
+                       /* Let go of our reservation. */
+                       btrfs_free_reserved_data_space(inode, last_byte -
+                                                      cur_offset);
                        if (ret < 0) {
                                free_extent_map(em);
                                break;
@@ -1685,8 +1697,6 @@ static long btrfs_fallocate(struct file *file, int mode,
        }
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, alloc_start, locked_end,
                             &cached_state, GFP_NOFS);
-
-       btrfs_free_reserved_data_space(inode, alloc_end - alloc_start);
 out:
        mutex_unlock(&inode->i_mutex);
        return ret;