LU-13651 hsm: call hsm_find_compatible_cb() only for cancel

LU-13651 hsm: call hsm_find_compatible_cb() only for cancel

The HSM action queue is scanned linearly in hsm_find_compatible_cb()
for existing requests on the same file so that duplicate or
conflicting requests are not added and cancel requests are assigned
the correct cookie, but this can cause a large delay in adding new
requests when the action queue is very large, as access to it is
locked for the duration of the search. Scanning the queue does not
guarantee that duplicate or conflicting requests are not added as
scanning (in hsm_find_compatible_cb()) and adding requests (in
mdt_agent_record_add()) are distinct operations that are not
serialized by a lock and so a race window exists between these two
function calls within which duplicate or conflicting requests can be
added. This is hopefully not a big problem though, as the CDT thread
will not send duplicate archive requests to a copytool serving a
different HSM backend (and it could probably be prevented from sending
duplicate archive requests to a copytool serving the same backend with
a small change in mdt_hsm_is_action_compat()) and duplicate restore
requests are serialized by taking the layout lock on the file before
being added to the action queue, which effectively serializes
them (although this blocks the caller, e.g. lfs, so it might not be
ideal). Since calling hsm_compatible_cb() does not protect completely
against this issue and can cause large delays in adding new requests,
we skip calling it for all requests apart from cancel requests that
don't specify a cookie (which should be all cancel requests in current
code), hopefully safely.

Test-Parameters: testlist=sanity-hsm
Signed-off-by: Kirill Malkin <kirill.malkin@hpe.com>
Signed-off-by: Nikitas Angelinas <nikitas.angelinas@hpe.com>
Signed-off-by: Sergey Cheremencev <sergey.cheremencev@hpe.com>
Cray-bug-id: LUS-8717
Change-Id: Id82b2a0720e46a9c12c4d9df323ce5a7bd7aff37
Reviewed-on: https://review.whamcloud.com/38867
Reviewed-by: Ben Evans <beevans@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Nathan Rutman <nrutman@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>