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From:   Pingfan Liu <kernelfans@gmail.com>
Date:   Mon, 29 Apr 2019 12:48:26 +0800
Message-ID: <CAFgQCTszGixzH5ZrwOzjbp7W91Wxo3XvA+EeEx0ErVVcYMr0FA@mail.gmail.com>
Subject: Re: [PATCHv2] kernel/crash: make parse_crashkernel()'s return value
 more indicant
To:     Dave Young <dyoung@redhat.com>
Cc:     Matthias Brugger <mbrugger@suse.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Rich Felker <dalias@libc.org>, linux-ia64@vger.kernel.org,
        Julien Thierry <julien.thierry@arm.com>,
        Yangtao Li <tiny.windzz@gmail.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Palmer Dabbelt <palmer@sifive.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>, x86@kernel.org,
        linux-mips@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-s390@vger.kernel.org,
        Florian Fainelli <f.fainelli@gmail.com>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        linux-sh@vger.kernel.org, Michael Ellerman <mpe@ellerman.id.au>,
        David Hildenbrand <david@redhat.com>,
        Russell King <linux@armlinux.org.uk>,
        Ingo Molnar <mingo@redhat.com>,
        linux-arm-kernel@lists.infradead.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        James Hogan <jhogan@kernel.org>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Will Deacon <will.deacon@arm.com>,
        linuxppc-dev@lists.ozlabs.org,
        Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
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        Hari Bathini <hbathini@linux.ibm.com>,
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        Baoquan He <bhe@redhat.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ralf Baechle <ralf@linux-mips.org>,
        Thomas Bogendoerfer <tbogendoerfer@suse.de>,
        Paul Burton <paul.burton@mips.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Logan Gunthorpe <logang@deltatee.com>,
        Greg Hackmann <ghackmann@android.com>,
        kexec@lists.infradead.org
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On Mon, Apr 29, 2019 at 11:04 AM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> On Sun, Apr 28, 2019 at 4:37 PM Dave Young <dyoung@redhat.com> wrote:
> >
> > On 04/25/19 at 04:20pm, Pingfan Liu wrote:
> > > On Wed, Apr 24, 2019 at 4:31 PM Matthias Brugger <mbrugger@suse.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.
> > > >
> > > It seems that kstrtoull() treats 0M as invalid parameter, while
> > > simple_strtoull() does not.
> > >
> > > If changed like your suggestion, then all the callers of memparse()
> > > will treats 0M as invalid parameter. This affects many components
> > > besides kexec.  Not sure this can be done or not.
> >
> > simple_strtoull is obsolete, move to kstrtoull is the right way.
> >
> > $ git grep memparse|wc
> >     158     950   10479
> >
> > Except some documentation/tools etc there are still a log of callers
> > which directly use the return value as the ull number without error
> > checking.
> >
> > So it would be good to mark memparse as obsolete as well in
> > lib/cmdline.c, and introduce a new function eg. kmemparse() to use
> > kstrtoull,  and return a real error code, and save the size in an
> > argument like &size.  Then update X86 crashkernel code to use it.
> >
> Thank for your good suggestion.
>
Go through the v5.0 kernel code, I think it will be a huge job.

The difference between unsigned long long simple_strtoull(const char
*cp, char **endp, unsigned int base) and int _kstrtoull(const char *s,
unsigned int base, unsigned long long *res) is bigger than expected,
especially the output parameter @res. Many references to
memparse(const char *ptr, char **retptr) rely on @retptr to work. A
typical example from arch/x86/kernel/e820.c
        mem_size = memparse(p, &p);
        if (p == oldp)
                return -EINVAL;

        userdef = 1;
        if (*p == '@') {  <----------- here
                start_at = memparse(p+1, &p);
                e820__range_add(start_at, mem_size, E820_TYPE_RAM);
        } else if (*p == '#') {
                start_at = memparse(p+1, &p);
                e820__range_add(start_at, mem_size, E820_TYPE_ACPI);
        } else if (*p == '$') {
                start_at = memparse(p+1, &p);
                e820__range_add(start_at, mem_size, E820_TYPE_RESERVED);
        }

So we need to resolve the prototype of kstrtoull() firstly, and maybe
kstrtouint() etc too. All of them have lots of references in kernel.

Any idea about this?

Thanks,
Pingfan