On Tue, 2010-07-20 at 22:29 -0500, Mike Christie wrote:
> On 07/20/2010 05:19 PM, Robert Love wrote:
> > From: Vasu Dev<vasu.dev@xxxxxxxxx>
> >
> > In this case, sync IO fails with EIO(5) errors as:-
> >
> > "Thread:1 System call error:5 - Input/output error (::pwrite() failed)".
> >
> > This is due to IO time out while libfc doing link down processing
> > to block all rports and if timed out IO was at last retry
> > attempt then it fails to user with EIO error followed by
> > these log messages.
> >
> > [77848.612169] host2: rport bf0015: Delete port
> > [77848.612221] host2: rport e10aef: work delete
> > [77848.612232] host2: rport e10002: work event 3
> > [77848.612422] sd 2:0:1:1: [sdi] Unhandled error code
> > [77848.612426] sd 2:0:1:1: [sdi] Result: hostbyte=DID_ERROR
> > driverbyte=DRIVER_OK
> > [77848.612431] sd 2:0:1:1: [sdi] CDB: Write(10): 2a 00 00 00 11 20 00 00 20 00
> > [77848.612445] end_request: I/O error, dev sdi, sector 4384
> > [77848.612553] sd 2:0:1:2: [sdj] Unhandled error code
> >
> > To fix these EIO errors, such timed out incomplete IOs needs
> > to be re-queued without counting retry attempt and this patch
> > does that using DID_REQUEUE scsi code.
> >
> > Signed-off-by: Vasu Dev<vasu.dev@xxxxxxxxx>
> > Signed-off-by: Robert Love<robert.w.love@xxxxxxxxx>
> > ---
> > drivers/scsi/libfc/fc_fcp.c | 5 +++++
> > 1 files changed, 5 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/scsi/libfc/fc_fcp.c b/drivers/scsi/libfc/fc_fcp.c
> > index a0a3ae7..61a1297 100644
> > --- a/drivers/scsi/libfc/fc_fcp.c
> > +++ b/drivers/scsi/libfc/fc_fcp.c
> > @@ -1971,6 +1971,11 @@ static void fc_io_compl(struct fc_fcp_pkt *fsp)
> > break;
> > }
> >
> > + if (lport->state != LPORT_ST_READY&& fsp->status_code != FC_COMPLETE) {
> > + sc_cmd->result = (DID_REQUEUE<< 16);
> > + FC_FCP_DBG(fsp, "Returning DID_REQUEUE to scsi-ml\n");
> > + }
> > +
>
> If it is a tape command, you do not want to use DID_REQUEUE do you?
>
I wasn't sure of using DID_REQUEUE here and therefore I did RFC first at
http://www.open-fcoe.org/pipermail/devel/2010-June/010360.html. As I
understand DID_REQUEUE would block the sdev and would do unconditional
retry and now I see that is issue with tapes as you pointed above, so
I'll remove its use here but help me understand use of DID_REQUEUE, I
mean are LLLD expected to make additional checks before indicating
DID_REQUEUE to scsi-ml ?
> You are using the fc class API to delete the rport in this scenario,
> right?
Yes.
> If so normally I think you would use DID_TRANSPORT_DISRUPTED.
> This is going to give you an error if it is the last retry like
> DID_ERROR though.
>
Effectively both would do same, so changing DID_TRANSPORT_DISRUPTED
won't change anything or perhaps I'm missing something here.
> It seems weird to try and work around the IO erorr in this case because
> it is the last retry so it should fail. If the port keeps going down and
> up, then with your patch you could keep retrying the IO forever.
>
I think last try should not fail due to link down if rports comes back
before dev_loss_tmo or fast_io_fail_tmo, such IOs should get their last
try attempt again once rport are back instead throwing IO error just
before port is getting blocked, that is the whole purpose of rport block
states.
> This isn't one of those races where you are blocking the rport, but the
> IO keeps coming around so the retries are used really quickly right (the
> driver looks like it has the fc class and internal state checks to
> prevent this but I wanted to make sure).
I'm trying to fix IO error due to failed last attempt on a IO just after
link down and its rport yet to move to block state from pending rport
event_work. The libfc already has checks once rport or lport no longer
ready for new IO try and that is not an issue here. It is very rare case
with very tiny time window as rport block, so I can replace DID_REQUEUE
here by DID_IMM_RETRY and I verified that works, will that be okay ?
This tiny time windows can be further reduced by use of wmb() on rport
state change to block and lport getting out of ready since their states
are checked w/o lock in queuecommand path. I can do that as separate
patch only if needed and it really helps some corner case.
Sorry for being late on this and I just noticed James just applied this
patch, so I'll provide separate patch to remove DID_REQUEUE for tape
devices.
Thanks
Vasu
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