ext4: warn when page is dirtied without buffers

Warn when a page is dirtied without buffers (as that will likely lead to
a crash in ext4_writepages()) or when it gets newly dirtied without the
page being locked (as there is nothing that prevents buffers to get
stripped just before calling set_page_dirty() under memory pressure).

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -3714,13 +3714,21 @@ static int ext4_journalled_set_page_dirty(struct page *page)
 	return __set_page_dirty_nobuffers(page);
 }
 
+static int ext4_set_page_dirty(struct page *page)
+{
+	WARN_ON_ONCE(!PageLocked(page) && !PageDirty(page));
+	WARN_ON_ONCE(!page_has_buffers(page));
+	return __set_page_dirty_buffers(page);
+}
+
 static const struct address_space_operations ext4_aops = {
 	.readpage		= ext4_readpage,
 	.readpages		= ext4_readpages,
 	.writepage		= ext4_writepage,
 	.writepages		= ext4_writepages,
 	.write_begin		= ext4_write_begin,
 	.write_end		= ext4_write_end,
+	.set_page_dirty		= ext4_set_page_dirty,
 	.bmap			= ext4_bmap,
 	.invalidatepage		= ext4_invalidatepage,
 	.releasepage		= ext4_releasepage,
@@ -3753,6 +3761,7 @@ static const struct address_space_operations ext4_da_aops = {
 	.writepages		= ext4_writepages,
 	.write_begin		= ext4_da_write_begin,
 	.write_end		= ext4_da_write_end,
+	.set_page_dirty		= ext4_set_page_dirty,
 	.bmap			= ext4_bmap,
 	.invalidatepage		= ext4_da_invalidatepage,
 	.releasepage		= ext4_releasepage,