libceph: request a new osdmap if lingering request maps to no osd
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: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org # 3.10+
Signed-off-by: Ilya Dryomov <152d4c5bebf13a5b809d42b4d789cf9d887e6698@gmail.com>
Reviewed-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs