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

[Pingfan Liu <kernelfans@gmail.com>]

On Fri, Apr 19, 2019 at 4:19 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> On Fri, 19 Apr 2019, Pingfan Liu wrote:
>
> > At present, both return and crash_size should be checked to guarantee the
> > success of parse_crashkernel().
> > Simplify the way by returning negative if fail, positive if success. In
> > case of failure, -EINVAL for bad syntax, -1 for the parsing results in
> > crash_size=0.
>
> I'm not entirely sure what you are trying to say here, but '-1' is not an
> improvement at all. We surely are not short of proper error codes, right?
>
The different negative return values are only used by x86. The option
"crashkernel=X,high", which is only used on x86, causes parse_kernel()
to return -EINVAL, then let parse_crashkernel_high() have a try.

When parsing crashkernel=size@offset and crashkernel=range1:size1,
there are other cases of failure, which is not worth to call
parse_crashkernel_high() to have a try. That is "-1" aiming for.

First, in parse_crashkernel_mem(), if demanded size is bigger than
system ram, this one looks like -ENOMEM, but -ENOMEM normally is used
for allocation. Second, in parse_crashkernel_mem(), if system ram is
not inside the range listed by "crashkernel=". Third, crashkernel=0MB
is given in the option (not in practice, but can not forbid user to do
so).

All of these cases can be treated as -EINVAL, but hard to define the
error codes.
> Also I don't see any positive return value > 0. So what is this about:
>
Yes. 0 is enough for success.  I had thought about returning 1 if
@offset is specified in crashkernel. But at present, no use case for
it.

> > --- a/arch/ia64/kernel/setup.c
> > +++ b/arch/ia64/kernel/setup.c
> > @@ -277,7 +277,7 @@ static void __init setup_crashkernel(unsigned long total, int *n)
> >
> >       ret = parse_crashkernel(boot_command_line, total,
> >                       &size, &base);
> > -     if (ret == 0 && size > 0) {
> > +     if (ret >= 0) {
>
>   ^^^^^^^^^^^^^^^^^^^^^^^^^^^  ????
>
> >       if (!memory_region_available(crash_base, crash_size)) {
> > diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> > index 45a8d0b..0b626e2 100644
> > --- a/arch/powerpc/kernel/fadump.c
> > +++ b/arch/powerpc/kernel/fadump.c
> > @@ -376,7 +376,7 @@ static inline unsigned long fadump_calculate_reserve_size(void)
> >        */
> >       ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> >                               &size, &base);
> > -     if (ret == 0 && size > 0) {
> > +     if (ret >= 0) {
>
> and this ?
>
> >               unsigned long max_size;
> >
> >               if (fw_dump.reserve_bootvar)
> > diff --git a/arch/powerpc/kernel/machine_kexec.c b/arch/powerpc/kernel/machine_kexec.c
> > index 63f5a93..9f3e61a 100644
> > --- a/arch/powerpc/kernel/machine_kexec.c
> > +++ b/arch/powerpc/kernel/machine_kexec.c
> > @@ -122,7 +122,7 @@ void __init reserve_crashkernel(void)
> >       /* use common parsing */
> >       ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> >                       &crash_size, &crash_base);
> > -     if (ret == 0 && crash_size > 0) {
> > +     if (ret >= 0) {
>
> Again.
>
> >               crashk_res.start = crash_base;
> >               crashk_res.end = crash_base + crash_size - 1;
> >       }
> > --- a/arch/sh/kernel/machine_kexec.c
> > +++ b/arch/sh/kernel/machine_kexec.c
> > @@ -157,7 +157,7 @@ void __init reserve_crashkernel(void)
> >
> >       ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> >                       &crash_size, &crash_base);
> > -     if (ret == 0 && crash_size > 0) {
> > +     if (ret >= 0) {
>
> And some more.
>
> >               crashk_res.start = crash_base;
> >               crashk_res.end = crash_base + crash_size - 1;
> >       }
> > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> > index 3d872a5..62d07d4 100644
> > --- a/arch/x86/kernel/setup.c
> > +++ b/arch/x86/kernel/setup.c
> > @@ -526,11 +526,11 @@ static void __init reserve_crashkernel(void)
> >
> >       /* crashkernel=XM */
> >       ret = parse_crashkernel(boot_command_line, total_mem, &crash_size, &crash_base);
> > -     if (ret != 0 || crash_size <= 0) {
> > +     if (ret == -EINVAL) {
>
> Without an explanation why this proceedes on error codes other than EINVAL
> this is uncomprehensible. Comments exist for a reason.
>
As explained above, deciding whether to let parse_crashkernel_high() try.

> >               /* crashkernel=X,high */
> >               ret = parse_crashkernel_high(boot_command_line, total_mem,
> >                                            &crash_size, &crash_base);
> > -             if (ret != 0 || crash_size <= 0)
> > +             if (ret < 0)
> >                       return;
> >               high = true;
>
> > @@ -87,7 +87,7 @@ static int __init parse_crashkernel_mem(char *cmdline,
> >               cur = tmp;
> >               if (size >= system_ram) {
> >                       pr_warn("crashkernel: invalid size\n");
> > -                     return -EINVAL;
> > +                     return -1;
>
> Well, this is incomprehensible as well. The pr_warn() says invalid and then
> you change the error code to something magic.
>
As explained above, want to know whether worth to let
parse_crashkernel_high() try.

What about the following alternative method? Treating crash_size=0 as
-EINVAL. Then on x86, just call parse_crashkernel_high() blindly to
have a try. Thanks for your review.

Regards,
Pingfan