Patch "libceph: don't bail early from try_read() when skipping a message" has been added to the 4.4-stable tree

Patch "libceph: don't bail early from try_read() when skipping a message" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

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

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     libceph-don-t-bail-early-from-try_read-when-skipping-a-message.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From e7a88e82fe380459b864e05b372638aeacb0f52d Mon Sep 17 00:00:00 2001
From: Ilya Dryomov <idryomov@gmail.com>
Date: Wed, 17 Feb 2016 20:04:08 +0100
Subject: libceph: don't bail early from try_read() when skipping a message

From: Ilya Dryomov <idryomov@gmail.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@sandisk.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Tested-by: Varada Kari <Varada.Kari@sandisk.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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);


Patches currently in stable-queue which might be from idryomov@gmail.com are

queue-4.4/libceph-fix-ceph_msg_revoke.patch
queue-4.4/tcp-dccp-fix-another-race-at-listener-dismantle.patch
queue-4.4/libceph-don-t-spam-dmesg-with-stray-reply-warnings.patch
queue-4.4/libceph-don-t-bail-early-from-try_read-when-skipping-a-message.patch
queue-4.4/libceph-use-the-right-footer-size-when-skipping-a-message.patch