linux-kernel - Re: [RFC/RFT PATCH 1/5] s390: make crashk

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Message-ID: <1efc386c-2cb4-164f-7194-497f142f969f@redhat.com>
Date:   Tue, 1 Jun 2021 10:45:35 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Russell King <linux@...linux.org.uk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org
Subject: Re: [RFC/RFT PATCH 1/5] s390: make crashk_res resource a child of
 "System RAM"

On 31.05.21 14:29, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@...ux.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" ...

So once you make "Crash kernel" a child of "System RAM", kexec-tools 
would break if I'm not completely wrong.

-- 
Thanks,

David / dhildenb