linux-kernel - Re: [PATCH 3/3 V2] pvclock: Get rid of __pvclock_read_cycles in function pvclock_read

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Message-ID: <20160612114643.GA24066@localhost>
Date:	Sun, 12 Jun 2016 19:46:47 +0800
From:	Minfei Huang <mnghuan@...il.com>
To:	Borislav Petkov <bp@...e.de>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, luto@...nel.org,
	hpa@...or.com, mingo@...hat.com, tglx@...utronix.de,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3 V2] pvclock: Get rid of __pvclock_read_cycles in
 function pvclock_read_flags

On 06/09/16 at 01:28P, Borislav Petkov wrote:
> On Thu, Jun 09, 2016 at 01:21:18PM +0200, Paolo Bonzini wrote:
> > This is basically implementing a seqcount.  It needs two barriers and,
> 
> Why does it need the two barriers? More details please.

Hi, Borislav.

It's a seqcount-like. We should confirm that reading flags occurs
between two reading version. To make complier do not reorder, two
barriers are necessary.

Thanks
Minfei