linux-kernel - [PATCH] fs: warn if stale pagecache is left after direct write

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Date:   Mon, 28 Oct 2019 13:03:06 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: [PATCH] fs: warn if stale pagecache is left after direct write

Function generic_file_direct_write() tries to invalidate pagecache after
O_DIRECT write. Unlike to similar code in dio_complete() this silently
ignores error returned from invalidate_inode_pages2_range().

According to comment this code here because not all filesystems call
dio_complete() or do proper invalidation after O_DIRECT write.
Noticeable case is a blkdev_direct_IO().

This patch calls dio_warn_stale_pagecache() if invalidation fails.

Also this skips invalidation for async writes (written == -EIOCBQUEUED).
Async write should call dio_complete() later, when write completes.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
---
 mm/filemap.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 92abf5f348a9..1fa8d587ef78 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3222,11 +3222,15 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
 	 * Most of the time we do not need this since dio_complete() will do
 	 * the invalidation for us. However there are some file systems that
 	 * do not end up with dio_complete() being called, so let's not break
-	 * them by removing it completely
+	 * them by removing it completely.
+	 *
+	 * Noticeable case is a blkdev_direct_IO().
+	 *
+	 * Skip invalidation for async writes or if mapping has no pages.
 	 */
-	if (mapping->nrpages)
-		invalidate_inode_pages2_range(mapping,
-					pos >> PAGE_SHIFT, end);
+	if (written > 0 && mapping->nrpages &&
+	    invalidate_inode_pages2_range(mapping, pos >> PAGE_SHIFT, end))
+		dio_warn_stale_pagecache(file);
 
 	if (written > 0) {
 		pos += written;