linux-kernel - Re: [PATCHv2] kernel/crash: make parse_crashkernel()'s return value more indicant

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Date:   Thu, 2 May 2019 14:22:06 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Matthias Brugger <mbrugger@...e.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Rich Felker <dalias@...c.org>,
        linux-ia64@...r.kernel.org,
        Julien Thierry <julien.thierry@....com>,
        Yangtao Li <tiny.windzz@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>, x86@...nel.org,
        linux-mips@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        "H. Peter Anvin" <hpa@...or.com>, linux-s390@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        linux-sh@...r.kernel.org, Michael Ellerman <mpe@...erman.id.au>,
        David Hildenbrand <david@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        James Hogan <jhogan@...nel.org>,
        Dave Young <dyoung@...hat.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Will Deacon <will.deacon@....com>,
        linuxppc-dev@...ts.ozlabs.org,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Borislav Petkov <bp@...en8.de>, Stefan Agner <stefan@...er.ch>,
        Thomas Gleixner <tglx@...utronix.de>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Jens Axboe <axboe@...nel.dk>, Tony Luck <tony.luck@...el.com>,
        Baoquan He <bhe@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Robin Murphy <robin.murphy@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Thomas Bogendoerfer <tbogendoerfer@...e.de>,
        Paul Burton <paul.burton@...s.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Greg Hackmann <ghackmann@...roid.com>
Subject: Re: [PATCHv2] kernel/crash: make parse_crashkernel()'s return value
 more indicant

On Thu, Apr 25, 2019 at 4:20 PM Pingfan Liu <kernelfans@...il.com> wrote:
>
> On Wed, Apr 24, 2019 at 4:31 PM Matthias Brugger <mbrugger@...e.com> wrote:
> >
> >
> [...]
> > > @@ -139,6 +141,8 @@ static int __init parse_crashkernel_simple(char *cmdline,
> > >               pr_warn("crashkernel: unrecognized char: %c\n", *cur);
> > >               return -EINVAL;
> > >       }
> > > +     if (*crash_size == 0)
> > > +             return -EINVAL;
> >
> > This covers the case where I pass an argument like "crashkernel=0M" ?
> > Can't we fix that by using kstrtoull() in memparse and check if the return value
> > is < 0? In that case we could return without updating the retptr and we will be
> > fine.
After a series of work, I suddenly realized that it can not be done
like this way. "0M" causes kstrtoull() to return -EINVAL, but this is
caused by "M", not "0". If passing "0" to kstrtoull(), it will return
0 on success.

> >
> It seems that kstrtoull() treats 0M as invalid parameter, while
> simple_strtoull() does not.
>
My careless going through the code. And I tested with a valid value
"256M" using kstrtoull(), it also returned -EINVAL.

So I think there is no way to distinguish 0 from a positive value
inside this basic math function.
Do I miss anything?

Thanks and regards,
Pingfan