linux-kernel - Re: [Xen-devel] [PATCH] xen: Add comment for missing FROZEN notifier transitions

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Message-ID: <alpine.DEB.2.10.1604061652230.31453@sstabellini-ThinkPad-X230>
Date:	Wed, 6 Apr 2016 16:52:34 -0700 (PDT)
From:	Stefano Stabellini <sstabellini@...nel.org>
To:	Juergen Gross <jgross@...e.com>
cc:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Julien Grall <julien.grall@....com>,
	Anna-Maria Gleixner <anna-maria@...utronix.de>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
	sstabellini@...nel.org, rt@...utronix.de
Subject: Re: [Xen-devel] [PATCH] xen: Add comment for missing FROZEN notifier
 transitions

On Tue, 5 Apr 2016, Juergen Gross wrote:
> On 04/04/16 18:48, Boris Ostrovsky wrote:
> > On 04/04/2016 12:30 PM, David Vrabel wrote:
> >> On 04/04/16 17:21, Julien Grall wrote:
> >>> (CC Stefano new e-mail address)
> >>>
> >>> Hello Anna-Maria,
> >>>
> >>> On 04/04/2016 13:32, Anna-Maria Gleixner wrote:
> >>>> Xen guests do not offline/online CPUs during suspend/resume and
> >>>> therefore FROZEN notifier transitions are not required. Add this
> >>>> explanation as a comment in the code to get not confused why
> >>>> CPU_TASKS_FROZEN masked transitions are not considered.
> >> Alternatively, these could be added even if they are not encountered.
> >> This might be more future-proof but the documentation might be clearer.
> >>
> >> Boris, Juergen, any opinion?
> 
> I'd rather do more than a comment:
> 
> Either mask CPU_TASKS_FROZEN from action if it really doesn't matter
> whether the flag is set or not (which IMHO is the case here), or
> BUG_ON(action & CPU_TASKS_FROZEN) if this really should never happen.

I agree