Re: [PATCH 00/11] First pass at merging Bart's HA work

[Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>]

On 12/05/12 19:23, Or Gerlitz wrote:
> On Fri, Nov 30, 2012 at 4:21 AM, David Dillow <dillowda-1Heg1YXhbW8@public.gmane.org> wrote:
> [...]
>> Modulo a few style issues (braces around one line if branches, etc.) and
>> having three state variables vs one, I can live with everything up to
>> aabfa852acd27962 at git://github.com/bvanassche/linux.git#srp-ha. Those
>> two are small things that can be fixed later and are not worth holding
>> things up any further.
>>
>> I'll try to spend some time on the final four patches tomorrow afternoon.
>
> Dave, Bart
>
> My colleague Alex Turin <alextu-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> tried  today the bits as
> they appear in Roland's kernel.org tree / for-next branch up to commit
>   fb57e1dbbd4 and here's some feedback
>
> Basically, what he did was connecting  to a target, next take down the
> IB port on the initiator side, and issue some IOs (dd if=/dev/sdb
> of=/dev/null count=1)
>
> Our recollection of events from the logs (below) is the following
>
> 1. queued command get completion status 5
>
> 2. as part of error handling srp_reset_host() was called,
>
> 3. srp_reset_host() calls to srp_reconnect_target() which fails cause
> port is down.
>
> 4. srp_reconnect_target() on failure calls to srp_queue_remove_work()
> which sets
> target->status to SRP_TARGET_REMOVED.
>
> 5.srp_reset_host() called second time. it calls to
> srp_reconnect_target() but target->state == SRP_TARGET_REMOVED.
> srp_reconnect_target() checks if target->state != SRP_TARGET_LIVE and
> return -EAGAIN.
>
> This probably means that even after enabling port it will still fail
> to reconnect?

Hello Or,

The only way to make I/O work reliably if a failure can occur at the 
transport layer is to use multipathd on top of ib_srp. If a connection 
fails for some reason, then the SRP SCSI host will be removed after the 
SCSI error handler has finished with its error recovery strategy. And 
once the transport layer is operational again and srp_daemon detects 
that the initiator is no longer logged in srp_daemon will make ib_srp 
log in again. multipathd will then cause I/O to continue over the new path.

Bart.

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