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    SubjectRe: [PATCHv2] kernel/crash: make parse_crashkernel()'s return value more indicant
    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 simple_strtoull is obsolete, move to kstrtoull is the right way.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

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