linux-kernel - Re: [PATCH] [RFC] arm64: export this_cpu_has

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Message-ID: <CANLsYkyQssRivPCPJQf11UeUwp089byhpB1MvoGy50r3Yz+ULQ@mail.gmail.com>
Date:   Mon, 1 Nov 2021 09:32:29 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Arnd Bergmann <arnd@...db.de>, Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        David Brazdil <dbrazdil@...gle.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RFC] arm64: export this_cpu_has_cap

On Mon, 1 Nov 2021 at 05:13, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Mon, Nov 01, 2021 at 09:52:22AM +0000, Suzuki K Poulose wrote:
> > On 01/11/2021 09:40, Will Deacon wrote:
> > > On Mon, Nov 01, 2021 at 09:34:08AM +0000, Suzuki K Poulose wrote:
> > > > On 01/11/2021 09:01, Will Deacon wrote:
> > > > > On Fri, Oct 29, 2021 at 07:06:23PM +0100, Catalin Marinas wrote:
> > > > > > On Fri, Oct 29, 2021 at 02:31:23PM +0100, Suzuki K Poulose wrote:
> > > > > > > On 29/10/2021 12:30, Arnd Bergmann wrote:
> > > > > > > > From: Arnd Bergmann <arnd@...db.de>
> > > > > > > >
> > > > > > > > It's now used in a coresight driver that can be a loadable module:
> > > > > > > >
> > > > > > > > ERROR: modpost: "this_cpu_has_cap" [drivers/hwtracing/coresight/coresight-trbe.ko] undefined!
> > > > > > > >
> > > > > > > > Fixes: 8a1065127d95 ("coresight: trbe: Add infrastructure for Errata handling")
> > > > > > >
> > > > > > > Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
> > > > > > > Tested-by: Suzuki K Poulose <suzuki.poulose@....com>
> > > > > > >
> > > > > > > Will, Catalin, Mathieu,
> > > > > > >
> > > > > > > Do you have a preference on how this fix can be pulled in ? This may
> > > > > > > be safe to go via coresight tree if it is not too late. Otherwise,
> > > > > > > it could go via the arm64 tree.
> > > > > >
> > > > > > I think Will already closed/tagged the arm64 tree for the upcoming
> > > > > > merging window, though he could take it as a fix afterwards.
> > > > > >
> > > > > > If it doesn't conflict with the arm64 for-next/core, it's fine by me to
> > > > > > go through the coresight tree.
> > > > > >
> > > > > > > > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > > > > > > > ---
> > > > > > > > Not sure if we actually want this to be exported, this is my local
> > > > > > > > workaround for the randconfig build bot.
> > > > > > > > ---
> > > > > > > >     arch/arm64/kernel/cpufeature.c | 1 +
> > > > > > > >     1 file changed, 1 insertion(+)
> > > > > > > >
> > > > > > > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > > > > > > > index ecbdff795f5e..beccbcfa7391 100644
> > > > > > > > --- a/arch/arm64/kernel/cpufeature.c
> > > > > > > > +++ b/arch/arm64/kernel/cpufeature.c
> > > > > > > > @@ -2864,6 +2864,7 @@ bool this_cpu_has_cap(unsigned int n)
> > > > > > > >           return false;
> > > > > > > >     }
> > > > > > > > +EXPORT_SYMBOL(this_cpu_has_cap);
> > > > > >
> > > > > > EXPORT_SYMBOL_GPL? I think this_cpu_has_cap() is a bit more more
> > > > > > specialised than cpus_have_const_cap().
> > > > > >
> > > > > > With that:
> > > > > >
> > > > > > Acked-by: Catalin Marinas <catalin.marinas@....com>
> > > > >
> > > > > Yes, at this stage I think it's best for this to go via the Coresight tree.
> > > > > So with the _GPL export:
> > > > >
> > > > > Acked-by: Will Deacon <will@...nel.org>
> > > > >
> > > > > If that doesn't work for some reason, I can take it next week after the
> > > > > initial arm64 queue has been merged. Please just let me know.
> > > >
> > > > As I understand correctly, this will now need to go via arm64 tree. The
> > > > CoreSight tree changes are pulled into Greg's tree and the next it will
> > > > happen is for the next release. Usually the fixes don't end up there
> > > > during the -rc cycles. So, I believe it is better if this goes via
> > > > arm64.
> > >
> > > Hmm, are you saying that Coresight drivers don't receive fixes outside of
> > > the merge window? That sounds sub-optimal...
> >
> > Unfortunately thats how it works today. We should fix this.
> >
> > Mathieu, Greg,
> >
> > Do you have any thoughts on how to address this ?
>
> What?  That's crazy, if there are bugfixes needed of course I would take
> them during the -rc cycle, that is explicitly what it is there for!

I have sent patches to the char-misc tree several times during -rc
cycles.  As Greg points out, proceeding otherwise would not make
sense.

>
> It's up to the maintainer of the subsystem to send me the fixes to get
> into the -final kernel release, I don't pick them up on my own unless
> asked to by them.
>

I will send a pull request for this when I receive another patch with
Catalin's annotation and collected RB tags.

> thanks,
>
> greg k-h