On Mon, Jul 27, 2015 at 10:11 AM, James Bottomley
<James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, 2015-07-27 at 08:48 -0700, Dan Williams wrote:
>> On Mon, Jul 27, 2015 at 8:17 AM, James Bottomley
>> <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> > On Wed, 2015-07-22 at 14:08 -0700, Dan Williams wrote:
>> >> On Wed, Jul 22, 2015 at 11:28 AM, James Bottomley
>> >> <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> >> >
>> >> >> }
>> >> >>
>> >> >> void sas_device_set_phy(struct domain_device *dev, struct sas_port *port)
>> >> >> diff --git a/drivers/scsi/libsas/sas_port.c b/drivers/scsi/libsas/sas_port.c
>> >> >> index d3c5297c6c89..9a25ae3a52a4 100644
>> >> >> --- a/drivers/scsi/libsas/sas_port.c
>> >> >> +++ b/drivers/scsi/libsas/sas_port.c
>> >> >> @@ -219,7 +219,6 @@ void sas_deform_port(struct asd_sas_phy *phy, int gone)
>> >> >>
>> >> >> if (port->num_phys == 1) {
>> >> >> sas_unregister_domain_devices(port, gone);
>> >> >> - sas_port_delete(port->port);
>> >> >> port->port = NULL;
>> >> >> } else {
>> >> >> sas_port_delete_phy(port->port, phy->phy);
>> >> >>
>> >> >
>> >> > This should become
>> >> >
>> >> > if (port->num_phys == 1)
>> >> > sas_unregister_domain_device(port, gone);
>> >> >
>> >> > sas_port_delete_phy(port->port, phy->phy);
>> >> >
>> >> > So we end up with a port scheduled for destruction with no phys rather
>> >> > than making the last phy association hang around until the DISCE
>> >> > workqueue runs.
>> >>
>> >> Sounds ok in theory.
>> >
>> > It's not really a choice. The specific problem you've introduced with
>> > this patch is failure to cope with link flutter: a deform and form event
>> > queued sequentially. In the new scheme you're trying to introduce, the
>> > destruct event gets queued from the deform but behind the form and the
>> > link flutter results in a dead link. I thought just forcing a zero phy
>> > port would fix this, but it won't, either the destruct has to run in the
>> > context of the deform event or the form has to be queued later than the
>> > destruct. I think coupled with the changes above, there needs to be
>> >
>> > if (port->port) {
>> > /* dying port, requeue form event */
>> > resend the PORTE_BYTES_DMAED event
>> > return
>> > }
>> >
>> > inside the unmatched port loop in sas_port_form() if nothing is found as
>> > well to close this.
>>
>> I think it's too late. Once the lldd has triggered libsas to start
>> tear down I seem to recall the lldd has the expectation that a new
>> PORTE_BYTES_DMAED triggers the creation of a new port instance for
>> that phy. Once the flutter reaches libsas the race is already lost
>> and the port needs to be torn down, but I would need to take a closer
>> look.
>
> I don't understand your reasoning. The expectation is that
> PORTE_BYTES_DMAED leads to port formation. The proposal detects that
> this event precedes DISCE_DESTRUCT for the port and requeues the event,
> now after DISC_DESTRUCT, so it gets acted on. Where is the problem?
>
Ah, I read "flutter" and mistakenly thought "debounce". You're
addressing the case where we're fully committed to the port going
down, but a "port up" event is injected between the "port down" and
"destruct" events. Yes, I agree re-queuing needs to happen, however
don't we now have queue re-order problem with respect to a new "port
down" event? It seems events need to be held off in-order while the
subordinate DISCE events are processed.
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