Re: [PATCH] scsi_transport_fc: handle transient error on multipath environment

Mike Christie
2010-02-12T18:03:32Z

On 02/12/2010 11:46 AM, Mike Christie wrote:
> - Maybe you want to instead hook something into the dm-mutlipath's
> request (no more bios like in 2004 :)). Can you set a timer on that
> level of request. If that times out then, dm-multipath could do
> something like call blk_abort_queue.

Some more detail. I was thinking maybe you could stack the timeout
handlers like is done for request_fn handlers or maybe the scsi cmd
would use the upper layer's timer somehow. Not sure... but at the least
I think we would not want both a scsi request and dm request timers
running at the same time.

Then for the error handling and timeout handling, most FC drivers have a
terminate_rport_io which works without having to block the entire host.
Those drivers could implement a newer eh where instead of firing the
code in scsi_error.c when a cmd times out, it would run
terminate_rport_io from some workqueue.

new dm request timed out()
-> scsi_timed_out
-> fc_timed_out()
{
run new eh from workqueue();
}

new_eh()
/* no new cmds should be started until we figure out what is going on */
block rport()
/* releases cmds upwards so they can run while we try to figure out
what is going on */
terminate_rport_io()
/* check if devices are ok */
send_tur()
if (tur failed)
start old scsi_error.c code to unjam us.
else
/* everything looks ok so let IO run to this path again */
unblock rport()

>
> I think the problem with blk_abort_queue might be that it stops all IO
> to the entire host where you probably just want to work on the remote
> port/path. For that you could call something like
> recover_transient_error. Maybe it could just be a call to
> terminate_rport_io from a workqueue though.