shmem: update folio if shmem_replace_page() updates the page

commit 9dfb3b8d655022760ca68af11821f1c63aa547c3 upstream.

If we allocate a new page, we need to make sure that our folio matches
that new page.

If we do end up in this code path, we store the wrong page in the shmem
inode's page cache, and I would rather imagine that data corruption
ensues.

This will be solved by changing shmem_replace_page() to
shmem_replace_folio(), but this is the minimal fix.

Link: https://lkml.kernel.org/r/20220730042518.1264767-1-willy@infradead.org
Fixes: da08e9b79323 ("mm/shmem: convert shmem_swapin_page() to shmem_swapin_folio()")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

mm/shmem.c

@@ -1771,6 +1771,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 
 	if (shmem_should_replace_folio(folio, gfp)) {
 		error = shmem_replace_page(&page, gfp, info, index);
+		folio = page_folio(page);
 		if (error)
 			goto failed;
 	}