Btrfs: add pinned extents to on-disk free space cache correctly

I got this while running xfstests:

[24256.836098] block group 317849600 has an wrong amount of free space
[24256.836100] btrfs: failed to load free space cache for block group 317849600

We should clamp the extent returned by find_first_extent_bit(),
so the start of the extent won't smaller than the start of the
block group.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 20 insertions, 21 deletions

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index ec23d43d0c35..01840ef95a32 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -838,7 +838,7 @@ int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
         struct io_ctl io_ctl;
         struct list_head bitmap_list;
         struct btrfs_key key;
-        u64 start, end, len;
+        u64 start, extent_start, extent_end, len;
         int entries = 0;
         int bitmaps = 0;
         int ret;
@@ -857,25 +857,12 @@ int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
                                      struct btrfs_free_cluster,
                                      block_group_list);
 
-        /*
-         * We shouldn't have switched the pinned extents yet so this is the
-         * right one
-         */
-        unpin = root->fs_info->pinned_extents;
-
         /* Lock all pages first so we can lock the extent safely. */
         io_ctl_prepare_pages(&io_ctl, inode, 0);
 
         lock_extent_bits(&BTRFS_I(inode)->io_tree, 0, i_size_read(inode) - 1,
                          0, &cached_state, GFP_NOFS);
 
-        /*
-         * When searching for pinned extents, we need to start at our start
-         * offset.
-         */
-        if (block_group)
-                start = block_group->key.objectid;
-
         node = rb_first(&ctl->free_space_offset);
         if (!node && cluster) {
                 node = rb_first(&cluster->root);
@@ -918,9 +905,20 @@ int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
          * We want to add any pinned extents to our free space cache
          * so we don't leak the space
          */
+
+        /*
+         * We shouldn't have switched the pinned extents yet so this is the
+         * right one
+         */
+        unpin = root->fs_info->pinned_extents;
+
+        if (block_group)
+                start = block_group->key.objectid;
+
         while (block_group && (start < block_group->key.objectid +
                                block_group->key.offset)) {
-                ret = find_first_extent_bit(unpin, start, &start, &end,
+                ret = find_first_extent_bit(unpin, start,
+                                            &extent_start, &extent_end,
                                             EXTENT_DIRTY);
                 if (ret) {
                         ret = 0;
@@ -928,20 +926,21 @@ int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
                 }
 
                 /* This pinned extent is out of our range */
-                if (start >= block_group->key.objectid +
+                if (extent_start >= block_group->key.objectid +
                     block_group->key.offset)
                         break;
 
-                len = block_group->key.objectid +
-                        block_group->key.offset - start;
-                len = min(len, end + 1 - start);
+                extent_start = max(extent_start, start);
+                extent_end = min(block_group->key.objectid +
+                                 block_group->key.offset, extent_end + 1);
+                len = extent_end - extent_start;
 
                 entries++;
-                ret = io_ctl_add_entry(&io_ctl, start, len, NULL);
+                ret = io_ctl_add_entry(&io_ctl, extent_start, len, NULL);
                 if (ret)
                         goto out_nospc;
 
-                start = end + 1;
+                start = extent_end;
         }
 
         /* Write out the bitmaps */