Btrfs: clear the extent uptodate bits during parent transid failures

If btrfs reads a block and finds a parent transid mismatch, it clears
the uptodate flags on the extent buffer, and the pages inside it.  But
we only clear the uptodate bits in the state tree if the block straddles
more than one page.

This is from an old optimization from to reduce contention on the extent
state tree.  But it is buggy because the code that retries a read from
a different copy of the block is going to find the uptodate state bits
set and skip the IO.

The end result of the bug is that we'll never actually read the good
copy (if there is one).

The fix here is to always clear the uptodate state bits, which is safe
because this code is only called when the parent transid fails.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 45ca8f9b0d61..a55fbe6252de 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3871,10 +3871,9 @@ int clear_extent_buffer_uptodate(struct extent_io_tree *tree,
 	num_pages = num_extent_pages(eb->start, eb->len);
 	clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
 
-	if (eb_straddles_pages(eb)) {
-		clear_extent_uptodate(tree, eb->start, eb->start + eb->len - 1,
-				      cached_state, GFP_NOFS);
-	}
+	clear_extent_uptodate(tree, eb->start, eb->start + eb->len - 1,
+			      cached_state, GFP_NOFS);
+
 	for (i = 0; i < num_pages; i++) {
 		page = extent_buffer_page(eb, i);
 		if (page)