[3.16.y-ckt stable] Patch "libceph: request a new osdmap if lingering request maps to no osd" has been added to staging queue

[Luis Henriques]

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

    libceph: request a new osdmap if lingering request maps to no osd

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-ckt13.

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

------

>From 164e3db2835b062a50db9884a32dbc0daacd4c60 Mon Sep 17 00:00:00 2001
From: Ilya Dryomov <idryomov at gmail.com>
Date: Mon, 11 May 2015 17:53:10 +0300
Subject: libceph: request a new osdmap if lingering request maps to no osd

commit b0494532214bdfbf241e94fabab5dd46f7b82631 upstream.

This commit does two things.  First, if there are any homeless
lingering requests, we now request a new osdmap even if the osdmap that
is being processed brought no changes, i.e. if a given lingering
request turned homeless in one of the previous epochs and remained
homeless in the current epoch.  Not doing so leaves us with a stale
osdmap and as a result we may miss our window for reestablishing the
watch and lose notifies.

MON=1 OSD=1:

    # cat linger-needmap.sh
    #!/bin/bash
    rbd create --size 1 test
    DEV=$(rbd map test)
    ceph osd out 0
    rbd map dne/dne # obtain a new osdmap as a side effect (!)
    sleep 1
    ceph osd in 0
    rbd resize --size 2 test
    # rbd info test | grep size -> 2M
    # blockdev --getsize $DEV -> 1M

N.B.: Not obtaining a new osdmap in between "osd out" and "osd in"
above is enough to make it miss that resize notify, but that is a
bug^Wlimitation of ceph watch/notify v1.

Second, homeless lingering requests are now kicked just like those
lingering requests whose mapping has changed.  This is mainly to
recognize that a homeless lingering request makes no sense and to
preserve the invariant that a registered lingering request is not
sitting on any of r_req_lru_item lists.  This spares us a WARN_ON,
which commit ba9d114ec557 ("libceph: clear r_req_lru_item in
__unregister_linger_request()") tried to fix the _wrong_ way.

Signed-off-by: Ilya Dryomov <idryomov at gmail.com>
Reviewed-by: Sage Weil <sage at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/ceph/osd_client.c | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
index 8cbd41f5c424..446548de09f8 100644
--- a/net/ceph/osd_client.c
+++ b/net/ceph/osd_client.c
@@ -1959,20 +1959,29 @@ static void kick_requests(struct ceph_osd_client *osdc, bool force_resend,
 		err = __map_request(osdc, req,
 				    force_resend || force_resend_writes);
 		dout("__map_request returned %d\n", err);
-		if (err == 0)
-			continue;  /* no change and no osd was specified */
 		if (err < 0)
 			continue;  /* hrm! */
-		if (req->r_osd == NULL) {
-			dout("tid %llu maps to no valid osd\n", req->r_tid);
-			needmap++;  /* request a newer map */
-			continue;
-		}
+		if (req->r_osd == NULL || err > 0) {
+			if (req->r_osd == NULL) {
+				dout("lingering %p tid %llu maps to no osd\n",
+				     req, req->r_tid);
+				/*
+				 * A homeless lingering request makes
+				 * no sense, as it's job is to keep
+				 * a particular OSD connection open.
+				 * Request a newer map and kick the
+				 * request, knowing that it won't be
+				 * resent until we actually get a map
+				 * that can tell us where to send it.
+				 */
+				needmap++;
+			}

-		dout("kicking lingering %p tid %llu osd%d\n", req, req->r_tid,
-		     req->r_osd ? req->r_osd->o_osd : -1);
-		__register_request(osdc, req);
-		__unregister_linger_request(osdc, req);
+			dout("kicking lingering %p tid %llu osd%d\n", req,
+			     req->r_tid, req->r_osd ? req->r_osd->o_osd : -1);
+			__register_request(osdc, req);
+			__unregister_linger_request(osdc, req);
+		}
 	}
 	reset_changed_osds(osdc);
 	mutex_unlock(&osdc->request_mutex);