On 3/11/2014 12:00 AM, Nicholas A. Bellinger wrote:
On Thu, 2014-03-06 at 16:05 +0200, sagi grimberg wrote:
On 3/6/2014 12:04 AM, Nicholas A. Bellinger wrote:
On Wed, 2014-03-05 at 14:12 +0200, Sagi Grimberg wrote:
On 3/5/2014 2:06 AM, Nicholas A. Bellinger wrote:
On Tue, 2014-03-04 at 17:17 +0200, Sagi Grimberg wrote:
On 3/4/2014 2:00 AM, Nicholas A. Bellinger wrote:
<SNIP>
<nod>, I noticed that as well during recent debugging.
However, AFAICT the RDMA_CM_EVENT_TIMEWAIT_EVENT doesn't (always) occur
on the target side after a RDMA_CM_EVENT_DISCONNECTED, and thus far I've
not been able to ascertain what's different about the shutdown sequence
that would make this happen, or not happen..
Any ideas..?
That's probably because the cm_id is destroyed before you get the event.
There is a specific
timout computation to get this event (see IB spec). If you will attempt
to disconnect while
the link is down (initiator won't receive it and send you disconnect
back), you should be able
to see this event. As I understand, in order to comply the spec, the QP
(and the cm_id afterwards)
should be destroyed only when getting this event and not before.
<nod>, thanks for the additional background.
So currently rdma_destroy_qp() + rdma_destroy_id() is being done via
isert_connect_release(), which occurs after the final isert_put_conn()
happens from either the RDMA_CM_EVENT_DISCONNECTED handler, or within
isert_free_conn() in one of the per connection kernel thread contexts
via iscsit_close_connection().
If I understand the above correctly, the isert_put_conn() should move
from the RDMA_CM_EVENT_DISCONNECTED handler into the TIMEWAIT_EVENT
handler, yes..?
Yes.
And it's safe to assume that DISCONNECTED will always occur before
TIMEWAIT_EVENT, right..?
DISCONNECTED event may not even come at all (in case the initiator
didn't call rdma_disconnect). no guarantees here..
But, if once we get the TIMEWAIT event, we destroy the qp and the
*cm_id*, we won't get any CM events at all.
As I understand, we don't even need to explicitly destroy the cm_id, we
can just return a non-zero return from cma_handler
for TIMEWAIT events which will cause rdma_cm to implicitly destroy the
cm_id.
Mmmm, if that's the case then I'm more confused about how reference
counting for isert_conn should work wrt TIMEWAIT_EVENT than before.. ;)
Yes, it is indeed confusing.
The below might be even more confusing... I'll try to simplify.
As mentioned earlier, the first isert_put_conn() occurs from the per
connection process context after calling rdma_disconnect(), and the
second from the disconnected event handler.
Your comment above would seem to indicate that iser-target code should
be waiting to receive TIMEWAIT_EVENT, instead of pro-actively calling
rdma_disconnect() to trigger the disconnect. Is that correct..?
Not instead. iser-target should call rdma_disconnect upon DISCONNECTED
event but
destroy the qp and cm_id when getting TIMEWAIT.
There is a matter of sending disconnect request/response and a matter of
when
to destroy the QP.
DISCONNECTED events are coming from 2 conditions:
static int cma_ib_handler()
{
...
case IB_CM_DREQ_RECEIVED: /* remote side sent a disconnect
request */
case IB_CM_DREP_RECEIVED: /* remote side responded our
disconnect request */
if (!cma_comp_exch(id_priv, RDMA_CM_CONNECT,
RDMA_CM_DISCONNECT))
goto out;
event.event = RDMA_CM_EVENT_DISCONNECTED;
break;
...
}
So regardless if iser_target initiated rdma_disconnect - once it gets
DISCONNECTED event
it should call it *again* to respond the initiator disconnect request
(rdma_disconnect sends
CM DREQ and if fails calls CM_DREP - this is to cover that both sides
will send DREQ and DREP).
The removal of the QP and cm_id should come once getting TIMEWAIT event.
Hope this wasn't even more confusing...
Sagi.
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