linux-kernel - [PATCH 4.4 264/342] libceph: dont bail early from try

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Message-Id: <20160301234536.429727564@linuxfoundation.org>
Date:	Tue, 01 Mar 2016 23:55:13 +0000
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	<linux-kernel@...r.kernel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<stable@...r.kernel.org>, Varada Kari <Varada.Kari@...disk.com>,
	Ilya Dryomov <idryomov@...il.com>,
	Alex Elder <elder@...aro.org>
Subject: [PATCH 4.4 264/342] libceph: dont bail early from try_read() when skipping a message

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

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

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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/ceph/messenger.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -2340,7 +2340,7 @@ static int read_partial_message(struct c
 		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);
@@ -2366,7 +2366,7 @@ static int read_partial_message(struct c
 				sizeof(m->footer);
 			con->in_tag = CEPH_MSGR_TAG_READY;
 			con->in_seq++;
-			return 0;
+			return 1;
 		}
 
 		BUG_ON(!con->in_msg);