linux-kernel - Re: arch/arm/kernel/setup.c fails to compile for NOMMU

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Message-ID: <20190311085208.GY5232@dhcp22.suse.cz>
Date:   Mon, 11 Mar 2019 09:52:08 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Stefan Agner <stefan@...er.ch>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-kernel-owner@...r.kernel.org
Subject: Re: arch/arm/kernel/setup.c fails to compile for NOMMU

On Tue 05-03-19 23:08:45, Stefan Agner wrote:
> Hi Michal,
> 
> On 06.04.2018 11:56, Michal Hocko wrote:
> > On Fri 25-08-17 08:45:40, Michal Hocko wrote:
> >> On Thu 24-08-17 17:17:41, Russell King - ARM Linux wrote:
> >> > On Fri, Aug 18, 2017 at 01:24:02PM +0200, Michal Hocko wrote:
> >> > > Hi Russel,
> >> > > I have a battery of configs for compile testing and for some time I've
> >> > > been seeing the following compilation error with nommu config (attached)
> >> > >
> >> > > arch/arm/kernel/setup.c: In function 'reserve_crashkernel':
> >> > > arch/arm/kernel/setup.c:1005:25: error: 'SECTION_SIZE' undeclared (first
> >> > > use in this function)
> >> > >              crash_size, SECTION_SIZE);
> >> > >
> >> > > I didn't get to look what is going on here, maybe my config is just too
> >> > > artificial but the primary reason is that SECTION_SIZE is not defined in
> >> > > pgtable-nommu.h. To be honest I am not familiar with nommu very much and
> >> > > it smells like the whole reserve_crashkernel doesn't really make any
> >> > > sense on those configs. Could you have a look what is the best fix
> >> > > please?
> >> >
> >> > Hi,
> >> >
> >> > I suspect that mach-netx has never been tested in nommu configurations
> >> > (ditto for many of the older platforms, which pre-date merging nommu
> >> > support.)
> >> >
> >> > Maybe the best solution is to make these old platforms depend on MMU.
> >> >
> >> > However, I'm wondering whether kexec makes sense for !MMU - that's
> >> > probably something that hasn't been tested and doesn't actually work.
> >> > So maybe another approach would be to make kexec depend on MMU for
> >> > ARM - but I'm afraid I don't really know.
> >>
> >> Yeah, I've disabled KEXEC in my testing config. All I do care about is
> >> to test nommu specific code paths in MM code.
> >>
> >> > I only have very limited nommu experience.
> >>
> >> me too
> >>
> >> So what would you say about the following?
> > 
> > It's been some time and it seems this has fallen between cracks. Is this
> > worth puruing or I should just forget about it and drop it on the floor?
> 
> I actually came across this issue during some randconfig testing. Your
> change looks good to me:
> 
> Reviewed-by: Stefan Agner <stefan@...er.ch>
> 
> Fixes for the ARM core usually go through Russell's patch tracker, did
> you submit you patch there?
> 
> See also:
> https://www.arm.linux.org.uk/developer/patches/info.php

Thanks! I am quite busy though so please feel free to resubmit if you
feel this is worth it.

> --
> Stefan
> 
> >> ---
> >> From 2707f3bf00181bbc9dcf6a1f287eb7369141e955 Mon Sep 17 00:00:00 2001
> >> From: Michal Hocko <mhocko@...e.com>
> >> Date: Fri, 25 Aug 2017 08:40:09 +0200
> >> Subject: [PATCH] arm: make kexec depend on MMU
> >>
> >> arm nommu config with KEXEC enabled doesn't compile
> >> arch/arm/kernel/setup.c: In function 'reserve_crashkernel':
> >> arch/arm/kernel/setup.c:1005:25: error: 'SECTION_SIZE' undeclared (first
> >> use in this function)
> >>              crash_size, SECTION_SIZE);
> >>
> >> since 61603016e212 ("ARM: kexec: fix crashkernel= handling") which is
> >> over one year without anybody noticing. I have only noticed beause of
> >> my testing nommu config which somehow gained CONFIG_KEXEC without
> >> an intention. This suggests that nobody is actually using KEXEC
> >> on nommu ARM configs. It is even a question whether kexec works with
> >> nommu.
> >>
> >> Make KEXEC depend on MMU to make this clear. If somebody wants to enable
> >> there will be probably more things to take care.
> >>
> >> Signed-off-by: Michal Hocko <mhocko@...e.com>
> >> ---
> >>  arch/arm/Kconfig | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> >> index 3f4aa9179337..c8603195d7fc 100644
> >> --- a/arch/arm/Kconfig
> >> +++ b/arch/arm/Kconfig
> >> @@ -2003,6 +2003,7 @@ config KEXEC
> >>  	bool "Kexec system call (EXPERIMENTAL)"
> >>  	depends on (!SMP || PM_SLEEP_SMP)
> >>  	depends on !CPU_V7M
> >> +	depends on MMU
> >>  	select KEXEC_CORE
> >>  	help
> >>  	  kexec is a system call that implements the ability to shutdown your
> >> --
> >> 2.13.2
> >>
> >> --
> >> Michal Hocko
> >> SUSE Labs

-- 
Michal Hocko
SUSE Labs