Commit dbfdb6d1b369 ("Btrfs: Search for all ordered extents that could
span across a page") make btrfs_invalidapage() to search all ordered
extents.
The offending code looks like this:
again:
start = page_start;
ordered = btrfs_lookup_ordered_range(inode, start, page_end - start +
1);
if (ordred) {
end = min(page_end,
ordered->file_offset + ordered->num_bytes - 1);
/* Do the cleanup */
start = end + 1;
if (start < page_end)
goto again;
}
The behavior is indeed necessary for the incoming subpage support, but
when it iterate through all the ordered extents, it also resets the
search range @start.
This means, for the following cases, we can double account the ordered
extents, causing its bytes_left underflow:
Page offset
0 16K 32K
|<--- OE 1 --->|<--- OE 2 ---->|
As the first iteration will find OE 1, which doesn't cover the full
page, thus after cleanup code, we need to retry again.
But again label will reset start to page_start, and we got OE 1 again,
which causes double account on OE1, and cause OE1's byte_left to
underflow.
The only good news is, this problem can only happen for subpage case, as
for regular sectorsize == PAGE_SIZE case, we will always find a OE ends
at or after page end, thus no way to trigger the problem.
This patch will move the again label after start = page_start, to fix
the bug.
This is just a quick fix, which is easy to backport.
There will be more comprehensive rework to convert the open coded loop to
a proper while loop.
Fixes: dbfdb6d1b369 ("Btrfs: Search for all ordered extents that could span
across a page")
Signed-off-by: Qu Wenruo <[email protected]>
---
fs/btrfs/inode.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index ef6cb7b620d0..2eea7d22405a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8184,8 +8184,9 @@ static void btrfs_invalidatepage(struct page *page,
unsigned int offset,
if (!inode_evicting)
lock_extent_bits(tree, page_start, page_end, &cached_state);
-again:
+
start = page_start;
+again:
ordered = btrfs_lookup_ordered_range(inode, start, page_end - start +
1);
if (ordered) {
found_ordered = true;
--
2.30.0
