linux-kernel - Re: [PATCH 2/5] hv: add helpers to handle hv

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Message-ID: <87y4g0hv4d.fsf@vitty.brq.redhat.com>
Date:	Mon, 21 Sep 2015 13:25:38 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Olaf Hering <olaf@...fle.de>
Cc:	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	apw@...onical.com, jasowang@...hat.com
Subject: Re: [PATCH 2/5] hv: add helpers to handle hv_util device state

Olaf Hering <olaf@...fle.de> writes:

> On Sun, Sep 20, Greg KH wrote:
>
>> Just use a lock, that's what it is there for.
>
> How would that help? It might help because it enforces ordering. But
> that requires that all three utils get refactored to deal with the
> introduced locking. I will let KY comment on this.
>
> The issue I see with fcopy is that after or while fcopy_respond_to_host
> runs an interrupt triggers which also calls into
> hv_fcopy_onchannelcallback.  It was most likely caused by a logic change
> in "recent" vmbus updates because this did not happen before. At least,
> the fcopy hang was not seen earler. Maybe the bug did just not trigger
> up to now for other reasons...

I'd like to see a trace from the hang, it is not obvious to me how it
happened and what caused it. (or if you have such hang scenario in your
head, can you please reveal it?) AFAICS barriers you introduced don't
give you guarantees in an SMP environment.

-- 
  Vitaly
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