linux-kernel - Re: [PATCH 03/12] powerpc: Replace cpu_up/down with device

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Message-ID: <20191119094747.4asxwnmyrjy5d5io@e107158-lin.cambridge.arm.com>
Date:   Tue, 19 Nov 2019 09:47:47 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Enrico Weigelt <info@...ux.net>, Ram Pai <linuxram@...ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/12] powerpc: Replace cpu_up/down with
 device_online/offline

On 11/19/19 12:19, Michael Ellerman wrote:
> Qais Yousef <qais.yousef@....com> writes:
> > The core device API performs extra housekeeping bits that are missing
> > from directly calling cpu_up/down.
> >
> > See commit a6717c01ddc2 ("powerpc/rtas: use device model APIs and
> > serialization during LPM") for an example description of what might go
> > wrong.
> >
> > This also prepares to make cpu_up/down a private interface for anything
> > but the cpu subsystem.
> >
> > Signed-off-by: Qais Yousef <qais.yousef@....com>
> > CC: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> > CC: Paul Mackerras <paulus@...ba.org>
> > CC: Michael Ellerman <mpe@...erman.id.au>
> > CC: Enrico Weigelt <info@...ux.net>
> > CC: Ram Pai <linuxram@...ibm.com>
> > CC: Nicholas Piggin <npiggin@...il.com>
> > CC: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
> > CC: Christophe Leroy <christophe.leroy@....fr>
> > CC: Thomas Gleixner <tglx@...utronix.de>
> > CC: linuxppc-dev@...ts.ozlabs.org
> > CC: linux-kernel@...r.kernel.org
> > ---
> >  arch/powerpc/kernel/machine_kexec_64.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> My initial though is "what about kdump", but that function is not called
> during kdump, so there should be no issue with the extra locking leading
> to deadlocks in a crash.
> 
> Acked-by: Michael Ellerman <mpe@...erman.id.au>

Thanks.

> 
> I assume you haven't actually tested it?

Only compile tested it I'm afraid. Would appreciate if you can give it a spin.
Otherwise I'd be happy to try it out on qemu.

Cheers

--
Qais Yousef