Re: [RFC/RFT PATCH 1/5] s390: make crashk_res resource a child of "System RAM"

From: Mike Rapoport <rppt@linux.ibm.com>
To: David Hildenbrand <david@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>,
	linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Russell King <linux@armlinux.org.uk>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Vasily Gorbik <gor@linux.ibm.com>, Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
	linux-mm@kvack.org, linux-s390@vger.kernel.org
Subject: Re: [RFC/RFT PATCH 1/5] s390: make crashk_res resource a child of "System RAM"
Date: Wed, 2 Jun 2021 09:25:14 +0300	[thread overview]
Message-ID: <YLckSuS3UuGbO7+p@linux.ibm.com> (raw)
In-Reply-To: <f6cd0c41-d7e2-65f5-94eb-9a21514df799@redhat.com>

On Tue, Jun 01, 2021 at 11:02:17AM +0200, David Hildenbrand wrote:
> On 01.06.21 10:45, David Hildenbrand wrote:
> > On 31.05.21 14:29, Mike Rapoport wrote:
> > > From: Mike Rapoport <rppt@linux.ibm.com>
> > > 
> > > Commit 4e042af463f8 ("s390/kexec: fix crash on resize of reserved memory")
> > > added a comment that says "crash kernel resource should not be part of the
> > > System RAM resource" but never explained why. As it looks from the code in
> > > the kernel and in kexec there is no actual reason for that.
> > 
> > Are you sure?
> > 
> > Looking at kexec-tools: kexec/arch/s390/kexec-s390.c
> > 
> > get_memory_ranges_s390() wants "System RAM" and Crash kernel only with
> > "with_crashk=1". Your patch would change that. "Crash kernel" would
> > always be included if you make it a child of "System RAM".
> > 
> > Further, get_memory_ranges() and is_crashkernel_mem_reserved() look out
> > for "Crash kernel\n" via parse_iomem_single().
> > 
> > However, parse_iomem_single() does not care about ranges that start with
> > spaces IIRC via
> >     sscanf(line, "%llx-%llx : %n" ...
> 
> I think I'm wrong about that one because I read
> 
> "Input white-space characters (as specified by the isspace function) are
> skipped, unless the specification includes a [ , c , or n specifier"
> 
> So having it as a child won't affect parse_iomem_single().

Yes, this was my understanding as well.

-- 
Sincerely yours,
Mike.

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