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Btrfs: clear the extent uptodate bits during parent transid failures

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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>
This commit is contained in:
Chris Mason 2012-02-22 12:36:24 -05:00
parent 16780cabb8
commit 5065319052
1 changed files with 3 additions and 4 deletions
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7
fs/btrfs/extent_io.c
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@ -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)