[PATCH 102/102] xfs: handle EOF correctly in xfs_vm_writepage

Dave Chinner
2012-08-23T05:05:16Z

From: Christoph Hellwig <hch@infradead.org>

Upstream commit: 6b7a03f03a2f8b1629133e35729eba4727fae3cc

We need to zero out part of a page which beyond EOF before setting uptodate,
otherwise, mapread or write will see non-zero data beyond EOF.

Based on the code in fs/buffer.c and the following ext4 commit:

ext4: handle EOF correctly in ext4_bio_write_page()

And yes, I wish we had a good test case for it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
---
fs/xfs/linux-2.6/xfs_aops.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/linux-2.6/xfs_aops.c b/fs/xfs/linux-2.6/xfs_aops.c
index 42eaf00..8c2ed74 100644
--- a/fs/xfs/linux-2.6/xfs_aops.c
+++ b/fs/xfs/linux-2.6/xfs_aops.c
@@ -978,11 +978,26 @@ xfs_vm_writepage(
end_index = offset >> PAGE_CACHE_SHIFT;
last_index = (offset - 1) >> PAGE_CACHE_SHIFT;
if (page->index >= end_index) {
- if ((page->index >= end_index + 1) ||
- !(i_size_read(inode) & (PAGE_CACHE_SIZE - 1))) {
+ unsigned offset_into_page = offset & (PAGE_CACHE_SIZE - 1);
+
+ /*
+ * Just skip the page if it is fully outside i_size, e.g. due
+ * to a truncate operation that is in progress.
+ */
+ if (page->index >= end_index + 1 || offset_into_page == 0) {
unlock_page(page);
return 0;
}
+
+ /*
+ * The page straddles i_size. It must be zeroed out on each
+ * and every writepage invocation because it may be mmapped.
+ * "A file is mapped in multiples of the page size. For a file
+ * that is not a multiple of the page size, the remaining
+ * memory is zeroed when mapped, and writes to that region are
+ * not written out to the file."
+ */
+ zero_user_segment(page, offset_into_page, PAGE_CACHE_SIZE);
}

end_offset = min_t(unsigned long long,