mm/filemap: don't relock the page after calling readpage

We don't need to get the page lock again; we just need to wait for the I/O
to finish, so use wait_on_page_locked_killable() like the other callers of
->readpage.

Link: https://lkml.kernel.org/r/20210122160140.223228-17-willy@infradead.orgSigned-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NKent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -2214,23 +2214,16 @@ static int filemap_read_page(struct file *file, struct address_space *mapping,
 	error = mapping->a_ops->readpage(file, page);
 	if (error)
 		return error;
-	if (PageUptodate(page))
-		return 0;
 
-	error = lock_page_killable(page);
+	error = wait_on_page_locked_killable(page);
 	if (error)
 		return error;
-	if (!PageUptodate(page)) {
-		if (page->mapping == NULL) {
-			/* page truncated */
-			error = AOP_TRUNCATED_PAGE;
-		} else {
+	if (PageUptodate(page))
+		return 0;
+	if (!page->mapping)	/* page truncated */
+		return AOP_TRUNCATED_PAGE;
 	shrink_readahead_size_eio(&file->f_ra);
-			error = -EIO;
-		}
-	}
-	unlock_page(page);
-	return error;
+	return -EIO;
 }
 
 static bool filemap_range_uptodate(struct address_space *mapping,