[PATCH] fs: fix lost error code in dio_complete

From: Maximilian Heyne <mheyne@amazon.de>
To: unlisted-recipients:; (no To-header on input)
Cc: Christoph Hellwig <hch@lst.de>,
	Maximilian Heyne <mheyne@amazon.de>, <stable@vger.kernel.org>,
	Torsten Mehlan <tomeh@amazon.de>, Uwe Dannowski <uwed@amazon.de>,
	Amit Shah <aams@amazon.de>, David Woodhouse <dwmw@amazon.co.uk>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	<linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: [PATCH] fs: fix lost error code in dio_complete
Date: Tue, 30 Oct 2018 21:57:39 +0000	[thread overview]
Message-ID: <20181030215739.4557-1-mheyne@amazon.de> (raw)

commit e259221763a40403d5bb232209998e8c45804ab8 ("fs: simplify the
generic_write_sync prototype") reworked callers of generic_write_sync(),
and ended up dropping the error return for the directio path. Prior to
that commit, in dio_complete(), an error would be bubbled up the stack,
but after that commit, errors passed on to dio_complete were eaten up.

This was reported on the list earlier, and a fix was proposed in
https://lore.kernel.org/lkml/20160921141539.GA17898@infradead.org/, but
never followed up with.  We recently hit this bug in our testing where
fencing io errors, which were previously erroring out with EIO, were
being returned as success operations after this commit.

The fix proposed on the list earlier was a little short -- it would have
still called generic_write_sync() in case `ret` already contained an
error.  This fix ensures generic_write_sync() is only called when
there's no pending error in the write.

CC: stable@vger.kernel.org
Reported-by: Ravi Nankani <rnankani@amazon.com>
Signed-off-by: Maximilian Heyne <mheyne@amazon.de>
Signed-off-by: Torsten Mehlan <tomeh@amazon.de>
Signed-off-by: Uwe Dannowski <uwed@amazon.de>
Signed-off-by: Amit Shah <aams@amazon.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 fs/direct-io.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 093fb54cd316..199146036093 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -325,8 +325,8 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, unsigned int flags)
 		 */
 		dio->iocb->ki_pos += transferred;
 
-		if (dio->op == REQ_OP_WRITE)
-			ret = generic_write_sync(dio->iocb,  transferred);
+		if (ret > 0 && dio->op == REQ_OP_WRITE)
+			ret = generic_write_sync(dio->iocb, ret);
 		dio->iocb->ki_complete(dio->iocb, ret, 0);
 	}
 
-- 
2.16.2

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