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

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.

Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>

1 files changed, 20 insertions, 11 deletions

diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
index 41a4abc7e98e..31d4b1ebff01 100644
--- a/net/ceph/osd_client.c
+++ b/net/ceph/osd_client.c
@@ -2017,20 +2017,29 @@ 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);