Revert "ext4: fix data corruption for mmap writes"

This reverts commit 156b66c5bad7fa7621024c2537bfeb48e5a21da0.

1 files changed, 5 insertions, 19 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index a0e2489d7..1580220e9 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1938,29 +1938,15 @@ static int ext4_writepage(struct page *page,
 static int mpage_submit_page(struct mpage_da_data *mpd, struct page *page)
 {
 	int len;
-	loff_t size;
+	loff_t size = i_size_read(mpd->inode);
 	int err;
 
 	BUG_ON(page->index != mpd->first_page);
-	clear_page_dirty_for_io(page);
-	/*
-	 * We have to be very careful here!  Nothing protects writeback path
-	 * against i_size changes and the page can be writeably mapped into
-	 * page tables. So an application can be growing i_size and writing
-	 * data through mmap while writeback runs. clear_page_dirty_for_io()
-	 * write-protects our page in page tables and the page cannot get
-	 * written to again until we release page lock. So only after
-	 * clear_page_dirty_for_io() we are safe to sample i_size for
-	 * ext4_bio_write_page() to zero-out tail of the written page. We rely
-	 * on the barrier provided by TestClearPageDirty in
-	 * clear_page_dirty_for_io() to make sure i_size is really sampled only
-	 * after page tables are updated.
-	 */
-	size = i_size_read(mpd->inode);
-	if (page->index == size >> PAGE_SHIFT)
-		len = size & ~PAGE_MASK;
+	if (page->index == size >> PAGE_CACHE_SHIFT)
+		len = size & ~PAGE_CACHE_MASK;
 	else
-		len = PAGE_SIZE;
+		len = PAGE_CACHE_SIZE;
+	clear_page_dirty_for_io(page);
 	err = ext4_bio_write_page(&mpd->io_submit, page, len, mpd->wbc, false);
 	if (!err)
 		mpd->wbc->nr_to_write--;