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

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Message-ID: <20150921121706.GA9172@aepfle.de>
Date:	Mon, 21 Sep 2015 14:17:06 +0200
From:	Olaf Hering <olaf@...fle.de>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
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

On Mon, Sep 21, Vitaly Kuznetsov wrote:

> 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?)

There is no trace. I think fcopy_respond_to_host notifies the host,
which in turn triggers an interrupt right away which is processed while
fcopy_on_msg is executing somewhere between the return from
fcopy_respond_to_host and the call into hv_fcopy_onchannelcallback.

> AFAICS barriers you introduced don't give you guarantees in an SMP environment.

Happens to work on x86, and for this purpose. I will see how to add
locking around access to  state and context.

Olaf
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