From 4618123c32587e3bb0fba56bac02fc2d39b15415 Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Wed, 27 Jan 2021 14:38:48 +0800 Subject: [PATCH] btrfs: fix double accounting of ordered extent for subpage case in btrfs_invalidapge Commit 7d73d859e498 ("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 iterates 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 ordered extent (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 accounting on OE 1, and cause OE 1's byte_left to underflow. 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. Move the again label after start = page_start. There will be more comprehensive rework to convert the open coded loop to a proper while loop for subpage support. Fixes: 7d73d859e498 ("Btrfs: Search for all ordered extents that could span across a page") Reviewed-by: Filipe Manana Signed-off-by: Qu Wenruo Signed-off-by: David Sterba --- 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 589030cefd90b..680cd0eea6d1a 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -8183,8 +8183,9 @@ 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; -- 2.39.5