linux-kernel - RE: [PATCH] Drivers: hv: fix infinite wait when channel open timeouts

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Message-ID: <CY1PR0301MB0777145FF901BB9BEFC86AA5A0590@CY1PR0301MB0777.namprd03.prod.outlook.com>
Date:	Fri, 3 Jun 2016 20:05:12 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Haiyang Zhang" <haiyangz@...rosoft.com>
Subject: RE: [PATCH] Drivers: hv: fix infinite wait when channel open timeouts



> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> Sent: Friday, June 3, 2016 3:15 AM
> To: devel@...uxdriverproject.org
> Cc: linux-kernel@...r.kernel.org; KY Srinivasan <kys@...rosoft.com>; Haiyang
> Zhang <haiyangz@...rosoft.com>
> Subject: [PATCH] Drivers: hv: fix infinite wait when channel open timeouts
> 
> vmbus_teardown_gpadl() can result in infinite wait when it is called
> on 5 second timeout in vmbus_open(). The issue is caused by the fact
> that gpadl teardown operation won't ever succeed for an opened channel
> and the timeout isn't always enough. Increase the timeout to 15 seconds
> and add sending CHANNELMSG_CLOSECHANNEL message on timeout to make
> sure
> the channel is closed.
> 
> The other possible solution for the issue would be to remove the timeout
> in vmbus_open() making our wait infinite.

I think removing the timeout in vmbus_open() maybe the safest solution since
anything else is still racy. A timeout in vmbus_open() tells us nothing about the
state of the channel. As a guest, we can trust the host to respond to our request.

Regards,

K. Y