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authorFilipe Manana <fdmanana@suse.com>2014-10-27 09:19:52 +0000
committerChris Mason <clm@fb.com>2014-10-28 13:59:54 -0700
commitd05a2b4cd97071462e77e6a7a8f109c36307182a (patch)
tree076dd128134b948de2a8a00d4618efeff88ec791
parent5ed5f5884116e3841da626d201ef068f23232a3a (diff)
Btrfs: fix race that makes btrfs_lookup_extent_info miss skinny extent items
We have a race that can lead us to miss skinny extent items in the function btrfs_lookup_extent_info() when the skinny metadata feature is enabled. So basically the sequence of steps is: 1) We search in the extent tree for the skinny extent, which returns > 0 (not found); 2) We check the previous item in the returned leaf for a non-skinny extent, and we don't find it; 3) Because we didn't find the non-skinny extent in step 2), we release our path to search the extent tree again, but this time for a non-skinny extent key; 4) Right after we released our path in step 3), a skinny extent was inserted in the extent tree (delayed refs were run) - our second extent tree search will miss it, because it's not looking for a skinny extent; 5) After the second search returned (with ret > 0), we look for any delayed ref for our extent's bytenr (and we do it while holding a read lock on the leaf), but we won't find any, as such delayed ref had just run and completed after we released out path in step 3) before doing the second search. Fix this by removing completely the path release and re-search logic. This is safe, because if we seach for a metadata item and we don't find it, we have the guarantee that the returned leaf is the one where the item would be inserted, and so path->slots[0] > 0 and path->slots[0] - 1 must be the slot where the non-skinny extent item is if it exists. The only case where path->slots[0] is zero is when there are no smaller keys in the tree (i.e. no left siblings for our leaf), in which case the re-search logic isn't needed as well. This race has been present since the introduction of skinny metadata (change 3173a18f70554fe7880bb2d85c7da566e364eb3c). Signed-off-by: Filipe Manana <fdmanana@suse.com> Reviewed-by: Miao Xie <miaox@cn.fujitsu.com> Signed-off-by: Chris Mason <clm@fb.com>
-rw-r--r--fs/btrfs/extent-tree.c8
1 files changed, 0 insertions, 8 deletions
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 87c0b46f8a7e..a84e00da14f1 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -780,7 +780,6 @@ search_again:
else
key.type = BTRFS_EXTENT_ITEM_KEY;
-again:
ret = btrfs_search_slot(trans, root->fs_info->extent_root,
&key, path, 0, 0);
if (ret < 0)
@@ -796,13 +795,6 @@ again:
key.offset == root->nodesize)
ret = 0;
}
- if (ret) {
- key.objectid = bytenr;
- key.type = BTRFS_EXTENT_ITEM_KEY;
- key.offset = root->nodesize;
- btrfs_release_path(path);
- goto again;
- }
}
if (ret == 0) {