linux-kernel - RE: [PATCH 2/7] Drivers: hv: vmbus: Use READ_ONCE() to read variables that are volatile

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Message-ID: <CY1PR03MB213792CD8EFCF66E6E61CA09A09A0@CY1PR03MB2137.namprd03.prod.outlook.com>
Date:	Fri, 1 Apr 2016 22:02:42 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"vkuznets@...hat.com" <vkuznets@...hat.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>
Subject: RE: [PATCH 2/7] Drivers: hv: vmbus: Use READ_ONCE() to read variables
 that are volatile



> -----Original Message-----
> From: Greg KH [mailto:gregkh@...uxfoundation.org]
> Sent: Thursday, March 31, 2016 5:01 PM
> To: KY Srinivasan <kys@...rosoft.com>
> Cc: linux-kernel@...r.kernel.org; devel@...uxdriverproject.org;
> olaf@...fle.de; apw@...onical.com; vkuznets@...hat.com;
> jasowang@...hat.com
> Subject: Re: [PATCH 2/7] Drivers: hv: vmbus: Use READ_ONCE() to read
> variables that are volatile
> 
> On Wed, Mar 23, 2016 at 05:53:52PM -0700, K. Y. Srinivasan wrote:
> > Use the READ_ONCE macro to access variabes that can change
> asynchronously.
> 
> Why?  What is this "fixing"?

This is to prevent the compiler optimizations and moving the code. This is the
recommended mechanism for reading volatile variables. 

Regards,

K. Y
> 
> thanks,
> 
> greg k-h