linux-kernel - [PATCH 3.16.y-ckt 043/142] libceph: don't bail early from try

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Message-Id: <1458643271-4227-44-git-send-email-luis.henriques@canonical.com>
Date:	Tue, 22 Mar 2016 10:39:32 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Ilya Dryomov <idryomov@...il.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 043/142] libceph: don't bail early from try_read() when skipping a message

3.16.7-ckt26 -stable review patch.  If anyone has any objections, please let me know.

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

From: Ilya Dryomov <idryomov@...il.com>

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@...disk.com>
Signed-off-by: Ilya Dryomov <idryomov@...il.com>
Tested-by: Varada Kari <Varada.Kari@...disk.com>
Reviewed-by: Alex Elder <elder@...aro.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.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);