[3.16.y-ckt stable] Patch "libceph: don't bail early from try_read() when skipping a message" has been added to the 3.16.y-ckt tree

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    libceph: don't bail early from try_read() when skipping a message

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt26.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

---8<------------------------------------------------------------

>From c8f36e20e8e770768991f9ce22e089f85fad0044 Mon Sep 17 00:00:00 2001
From: Ilya Dryomov <idryomov at gmail.com>
Date: Wed, 17 Feb 2016 20:04:08 +0100
Subject: libceph: don't bail early from try_read() when skipping a message

commit e7a88e82fe380459b864e05b372638aeacb0f52d upstream.

The contract between try_read() and try_write() is that when called
each processes as much data as possible.  When instructed by osd_client
to skip a message, try_read() is violating this contract by returning
after receiving and discarding a single message instead of checking for
more.  try_write() then gets a chance to write out more requests,
generating more replies/skips for try_read() to handle, forcing the
messenger into a starvation loop.

Reported-by: Varada Kari <Varada.Kari at sandisk.com>
Signed-off-by: Ilya Dryomov <idryomov at gmail.com>
Tested-by: Varada Kari <Varada.Kari at sandisk.com>
Reviewed-by: Alex Elder <elder at linaro.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/ceph/messenger.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 6b15183a68c8..f2ea1a093800 100644
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -2285,7 +2285,7 @@ static int read_partial_message(struct ceph_connection *con)
 		con->in_base_pos = -front_len - middle_len - data_len -
 			sizeof(m->footer);
 		con->in_tag = CEPH_MSGR_TAG_READY;
-		return 0;
+		return 1;
 	} else if ((s64)seq - (s64)con->in_seq > 1) {
 		pr_err("read_partial_message bad seq %lld expected %lld\n",
 		       seq, con->in_seq + 1);
@@ -2318,7 +2318,7 @@ static int read_partial_message(struct ceph_connection *con)
 				sizeof(m->footer);
 			con->in_tag = CEPH_MSGR_TAG_READY;
 			con->in_seq++;
-			return 0;
+			return 1;
 		}

 		BUG_ON(!con->in_msg);