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authorChris Mason <chris.mason@oracle.com>2009-09-11 12:27:37 -0400
committerChris Mason <chris.mason@oracle.com>2009-09-11 13:31:07 -0400
commita1ed835e1ab5795f91b198d08c43e2f56848dcf3 (patch)
treeac3b370823fa76c5be7698e3663306badbbd622d /fs/btrfs/extent_map.c
parent8b62b72b26bcd72082c4a69d179dd906bcc22200 (diff)
Btrfs: Fix extent replacment race
Data COW means that whenever we write to a file, we replace any old extent pointers with new ones. There was a window where a readpage might find the old extent pointers on disk and cache them in the extent_map tree in ram in the middle of a given write replacing them. Even though both the readpage and the write had their respective bytes in the file locked, the extent readpage inserts may cover more bytes than it had locked down. This commit closes the race by keeping the new extent pinned in the extent map tree until after the on-disk btree is properly setup with the new extent pointers. Signed-off-by: Chris Mason <chris.mason@oracle.com>
Diffstat (limited to 'fs/btrfs/extent_map.c')
-rw-r--r--fs/btrfs/extent_map.c50
1 files changed, 50 insertions, 0 deletions
diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 72e9fa3c31f..5bc7a0d325e 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -198,6 +198,56 @@ static int mergable_maps(struct extent_map *prev, struct extent_map *next)
return 0;
}
+int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len)
+{
+ int ret = 0;
+ struct extent_map *merge = NULL;
+ struct rb_node *rb;
+ struct extent_map *em;
+
+ write_lock(&tree->lock);
+ em = lookup_extent_mapping(tree, start, len);
+
+ WARN_ON(em->start != start || !em);
+
+ if (!em)
+ goto out;
+
+ clear_bit(EXTENT_FLAG_PINNED, &em->flags);
+
+ if (em->start != 0) {
+ rb = rb_prev(&em->rb_node);
+ if (rb)
+ merge = rb_entry(rb, struct extent_map, rb_node);
+ if (rb && mergable_maps(merge, em)) {
+ em->start = merge->start;
+ em->len += merge->len;
+ em->block_len += merge->block_len;
+ em->block_start = merge->block_start;
+ merge->in_tree = 0;
+ rb_erase(&merge->rb_node, &tree->map);
+ free_extent_map(merge);
+ }
+ }
+
+ rb = rb_next(&em->rb_node);
+ if (rb)
+ merge = rb_entry(rb, struct extent_map, rb_node);
+ if (rb && mergable_maps(em, merge)) {
+ em->len += merge->len;
+ em->block_len += merge->len;
+ rb_erase(&merge->rb_node, &tree->map);
+ merge->in_tree = 0;
+ free_extent_map(merge);
+ }
+
+ free_extent_map(em);
+out:
+ write_unlock(&tree->lock);
+ return ret;
+
+}
+
/**
* add_extent_mapping - add new extent map to the extent tree
* @tree: tree to insert new map in