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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Greg Kurz" <groug@kaod.org>,
        "Michael S. Tsirkin" <mst@redhat.com>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
Message-ID: <lsq.1528380321.339285762@decadent.org.uk>
Subject: [PATCH 3.16 222/410] 9p/trans_virtio: discard zero-length reply
In-Reply-To: <lsq.1528380320.647747352@decadent.org.uk>
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3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Greg Kurz <groug@kaod.org>

commit 26d99834f89e76514076d9cd06f61e56e6a509b8 upstream.

When a 9p request is successfully flushed, the server is expected to just
mark it as used without sending a 9p reply (ie, without writing data into
the buffer). In this case, virtqueue_get_buf() will return len == 0 and
we must not report a REQ_STATUS_RCVD status to the client, otherwise the
client will erroneously assume the request has not been flushed.

Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/9p/trans_virtio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -164,7 +164,8 @@ static void req_done(struct virtqueue *v
 		p9_debug(P9_DEBUG_TRANS, ": rc %p\n", rc);
 		p9_debug(P9_DEBUG_TRANS, ": lookup tag %d\n", rc->tag);
 		req = p9_tag_lookup(chan->client, rc->tag);
-		p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
+		if (len)
+			p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
 	}
 }