linux-kernel - [PATCH 01/14] writeback: don't call mapping_set_error on AOP_WRITEPAGE

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Date: Thu, 15 Feb 2024 07:36:36 +0100
From: Christoph Hellwig <hch@....de>
To: linux-mm@...ck.org
Cc: Matthew Wilcox <willy@...radead.org>,
	Jan Kara <jack@...e.com>,
	David Howells <dhowells@...hat.com>,
	Brian Foster <bfoster@...hat.com>,
	Christian Brauner <brauner@...nel.org>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 01/14] writeback: don't call mapping_set_error on AOP_WRITEPAGE_ACTIVATE

mapping_set_error should only be called on 0 returns (which it ignores)
or a negative error code.

writepage_cb ends up being able to call writepage_cb on the magic
AOP_WRITEPAGE_ACTIVATE return value from ->writepage which means
success but the caller needs to unlock the page.  Ignore that and
just call mapping_set_error on negative errors.

(no fixes tag as this goes back more than 20 years over various renames
 and refactors so I've given up chasing down the original introduction)

Signed-off-by: Christoph Hellwig <hch@....de>
---
 mm/page-writeback.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 3f255534986a2f..703e83c69ffe08 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2535,7 +2535,9 @@ static int writepage_cb(struct folio *folio, struct writeback_control *wbc,
 {
 	struct address_space *mapping = data;
 	int ret = mapping->a_ops->writepage(&folio->page, wbc);
-	mapping_set_error(mapping, ret);
+
+	if (ret < 0)
+		mapping_set_error(mapping, ret);
 	return ret;
 }
 
-- 
2.39.2