Re: [PATCH 09/47] zfcp: open-code fc_block_scsi_eh() for host reset

Steffen Maier
2017-07-24T16:18:22Z

Hi Hannes,

unfortunately I only realized now by accident that there's stuff to
review. Would be nice to send it also explicitly to driver maintainers
in addition to the list.

Since you've asked for this multiple times, I happened to just now code
a patch series of 6 patches in order to decouple zfcp from scsi_cmnd for
device, target, and host reset.

While I provide some review comments below, I think it might be clearer
and easier to review if you would rebase your series on top of my
decoupling.

Let me know how urgent you'd like to see my code. I planned to send it
as RFC soon anyway. However, it hasn't seen any function testing yet. If
you don't care, let me know and I can send it.

On 06/28/2017 10:32 AM, Hannes Reinecke wrote:
> When issuing a host reset we should be waiting for all
> ports to become unblocked; just waiting for one might
> be resulting in host reset to return too early.
>
> Signed-off-by: Hannes Reinecke <hare@suse.com>
> ---
> drivers/s390/scsi/zfcp_scsi.c | 27 +++++++++++++++++++++++----
> 1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/s390/scsi/zfcp_scsi.c b/drivers/s390/scsi/zfcp_scsi.c
> index 0678cf7..3d18659 100644
> --- a/drivers/s390/scsi/zfcp_scsi.c
> +++ b/drivers/s390/scsi/zfcp_scsi.c
> @@ -311,13 +311,32 @@ static int zfcp_scsi_eh_target_reset_handler(struct scsi_cmnd *scpnt)
>
> static int zfcp_scsi_eh_host_reset_handler(struct scsi_cmnd *scpnt)
> {
> - struct zfcp_scsi_dev *zfcp_sdev = sdev_to_zfcp(scpnt->device);
> - struct zfcp_adapter *adapter = zfcp_sdev->port->adapter;
> - int ret;
> + struct Scsi_Host *host = scpnt->device->host;
> + struct zfcp_adapter *adapter = (struct zfcp_adapter *)host->hostdata[0];
> + int ret = 0;
> + unsigned long flags;
> + struct zfcp_port *port;
>
> zfcp_erp_adapter_reopen(adapter, 0, "schrh_1");
> zfcp_erp_wait(adapter);
> - ret = fc_block_scsi_eh(scpnt);
> +retry_rport_blocked:
> + spin_lock_irqsave(host->host_lock, flags);

missing read_lock(&adapter->port_list_lock);

Hm, well, I have to think about lock ordering, because my patch has the
port_list as outer loop and inside it calls fc_block_scsi_eh (also
modified with fc_rport as argument).
If there's any other location taking both locks we better get them in
the same order.

> + list_for_each_entry(port, &adapter->port_list, list) {
> + struct fc_rport *rport = port->rport;

port->rport can be NULL, so need to check

> +
> + if (rport->port_state == FC_PORTSTATE_BLOCKED) {
> + if (rport->flags & FC_RPORT_FAST_FAIL_TIMEDOUT)
> + ret = FAST_IO_FAIL;

Hm, doesn't this get lost if a next iteration hits ret=NEEDS_RETRY?

I was pondering in my own patch version what to return of just a subset
of ports ran into fast_io_fail. And for now I thought just fast_io_fail
would be good to let I/O bubble up for path failover, even if this would
include of rport which meanwhile unblocked properly and would not need
bubbling up pending requests because they could service them with a
simple retry.

> + else
> + ret = NEEDS_RETRY;
> + break;
> + }

Why do you open code fc_block_scsi_eh() instead of calling it with
port->rport (if it's !=NULL)?

Typically all rports would be blocked after adapter recovery, until they
become unblocked (via zfcp's async rport_work). So we can wait for each
in turn which should still only wait in summary for the last one to
unblock. E.g. if the first rport takes longest we wait for it, and the
rest of the loop will be fast since the others happen to be unblocked
(or fast_io_fail) already?

> + }

missing read_unlock(&adapter->port_list_lock);

> + spin_unlock_irqrestore(host->host_lock, flags);
> + if (ret == NEEDS_RETRY) {
> + msleep(1000);
> + goto retry_rport_blocked;
> + }
> if (ret)
> return ret;
>

--
Mit freundlichen Grüßen / Kind regards
Steffen Maier

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