linux-kernel - [PATCH 6.1 5/8] direct_write_fallback(): on error revert the ->ki

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Message-ID: <20251021070353.96705-7-mngyadam@amazon.de>
Date: Tue, 21 Oct 2025 09:03:40 +0200
From: Mahmoud Adam <mngyadam@...zon.de>
To: <stable@...r.kernel.org>
CC: <gregkh@...uxfoundation.org>, <nagy@...aternagy.com>, Al Viro
	<viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jens Axboe
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	<tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>, Jaegeuk Kim
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 Konishi" <konishi.ryusuke@...il.com>, "Matthew Wilcox (Oracle)"
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 Chamberlain" <mcgrof@...nel.org>, <linux-block@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <ceph-devel@...r.kernel.org>,
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Subject: [PATCH 6.1 5/8] direct_write_fallback(): on error revert the ->ki_pos update from buffered write

From: Al Viro <viro@...iv.linux.org.uk>

commit 8287474aa5ffb41df52552c4ae4748e791d2faf2 upstream.

If we fail filemap_write_and_wait_range() on the range the buffered write went
into, we only report the "number of bytes which we direct-written", to quote
the comment in there.  Which is fine, but buffered write has already advanced
iocb->ki_pos, so we need to roll that back.  Otherwise we end up with e.g.
write(2) advancing position by more than the amount it reports having written.

Fixes: 182c25e9c157 "filemap: update ki_pos in generic_perform_write"
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Message-Id: <20230827214518.GU3390869@...IV>
Signed-off-by: Christian Brauner <brauner@...nel.org>
Signed-off-by: Mahmoud Adam <mngyadam@...zon.de>
---
 fs/libfs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/libfs.c b/fs/libfs.c
index a5bbe8e31d6616..63bc52c20f7e03 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1615,6 +1615,7 @@ ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
 		 * We don't know how much we wrote, so just return the number of
 		 * bytes which were direct-written
 		 */
+		iocb->ki_pos -= buffered_written;
 		if (direct_written)
 			return direct_written;
 		return err;
-- 
2.47.3




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