arm: Is VFP hotplug notifiers wrong?

[okuno.kohji at jp.panasonic.com]

Dear Russel and Thomas,

Thank you for your quick response.
Thomas, do you create the patch?

Best regards,
 Kohji Okuno

> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx at linutronix.de]
> Sent: Tuesday, January 9, 2018 10:58 PM
> To: Russell King - ARM Linux
> Cc: Okuno Kohji (奥埜 貢士); linux-arm-kernel at lists.infradead.org
> Subject: Re: arm: Is VFP hotplug notifiers wrong?
> 
> On Tue, 9 Jan 2018, Russell King - ARM Linux wrote:
> 
> > On Tue, Jan 09, 2018 at 08:12:21PM +0900, Kohji Okuno wrote:
> > > Dear Thomas and all,
> > >
> > > Could you please confirm about the following commit, again?
> > >
> > > http://git.armlinux.org.uk/cgit/linux-arm.git/commit/arch/arm/vfp/vf
> > > pmodule.c?id=e5b61bafe70477e05e1dce0d6ca4ec181e23cb2a
> > >
> > >
> > > The avobe commit eliminated the following fix, I think.
> > >
> > > http://git.armlinux.org.uk/cgit/linux-arm.git/commit/arch/arm/vfp/vf
> > > pmodule.c?id=384b38b66947b06999b3e39a596d4f2fb94f77e4
> > >
> > >
> > > vfp_force_reload() called from vfp_dying_cpu() does not clear
> > > vfp_current_hw_state[cpu], because cpu stopper task does not own the
> > > context held in the VFP hardware.
> >
> > You are correct, tglx's patch was wrong, since the state in the CPU
> > may not be the current thread's state, so vfp_force_reload() may not
> > do anything.
> >
> > vfp_force_reload() forces the reload of the specified state for the
> > specified CPU.  What the original hotplug code did was to ensure that
> > the CPU's state would be reloaded when it came back up.
> >
> > I do wish that people wouldn't combine functional changes and cleanups
> > into one patch - it makes this kind of thing harder to spot in review
> > and also means when we encounter crap like this, it means we can't
> > simply revert the cleanup.
> 
> sorry about that....