linux-kernel - Re: [PATCH v2 2/2] reboot: fix parsing of reboot cpu number

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Message-ID: <20201102110107.GG20201@alley>
Date:   Mon, 2 Nov 2020 12:01:07 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Matteo Croce <mcroce@...ux.microsoft.com>
Cc:     linux-kernel@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
        Arnd Bergmann <arnd@...db.de>, Mike Rapoport <rppt@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Robin Holt <robinmholt@...il.com>
Subject: Re: [PATCH v2 2/2] reboot: fix parsing of reboot cpu number

On Sun 2020-11-01 02:57:40, Matteo Croce wrote:
> On Fri, Oct 30, 2020 at 3:30 PM Petr Mladek <pmladek@...e.com> wrote:
> >
> > On Tue 2020-10-27 14:35:45, Matteo Croce wrote:
> > > From: Matteo Croce <mcroce@...rosoft.com>
> > >
> > > The kernel cmdline reboot= argument allows to specify the CPU used
> > > for rebooting, with the syntax `s####` among the other flags, e.g.
> > >
> > >   reboot=soft,s4
> > >   reboot=warm,s31,force
> > >
> > > In the early days the parsing was done with simple_strtoul(), later
> > > deprecated in favor of the safer kstrtoint() which handles overflow.
> > >
> > > But kstrtoint() returns -EINVAL if there are non-digit characters
> > > in a string, so if this flag is not the last given, it's silently
> > > ignored as well as the subsequent ones.
> > >
> > > To fix it, revert the usage of simple_strtoul(), which is no longer
> > > deprecated, and restore the old behaviour.
> > >
> > > While at it, merge two identical code blocks into one.
> >
> > > --- a/kernel/reboot.c
> > > +++ b/kernel/reboot.c
> > > @@ -552,25 +552,19 @@ static int __init reboot_setup(char *str)
> > >
> > >               case 's':
> > >               {
> > > -                     int rc;
> > > -
> > > -                     if (isdigit(*(str+1))) {
> > > -                             rc = kstrtoint(str+1, 0, &reboot_cpu);
> > > -                             if (rc)
> > > -                                     return rc;
> > > -                             if (reboot_cpu >= num_possible_cpus()) {
> > > -                                     reboot_cpu = 0;
> > > -                                     return -ERANGE;
> > > -                             }
> > > -                     } else if (str[1] == 'm' && str[2] == 'p' &&
> > > -                                isdigit(*(str+3))) {
> > > -                             rc = kstrtoint(str+3, 0, &reboot_cpu);
> > > -                             if (rc)
> > > -                                     return rc;
> > > -                             if (reboot_cpu >= num_possible_cpus()) {
> > > -                                     reboot_cpu = 0;
> >
> >                                                      ^^^^^^
> >
> > > +                     int cpu;
> > > +
> > > +                     /*
> > > +                      * reboot_cpu is s[mp]#### with #### being the processor
> > > +                      * to be used for rebooting. Skip 's' or 'smp' prefix.
> > > +                      */
> > > +                     str += str[1] == 'm' && str[2] == 'p' ? 3 : 1;
> > > +
> > > +                     if (isdigit(str[0])) {
> > > +                             cpu = simple_strtoul(str, NULL, 0);
> > > +                             if (cpu >= num_possible_cpus())
> > >                                       return -ERANGE;
> > > -                             }
> > > +                             reboot_cpu = cpu;
> >
> > The original value stays when the new one is out of range. It is
> > small functional change that should get mentioned in the commit
> > message or better fixed separately.

Ah, I see. From some reason, I assumed that it was defined as
module_param() or core_param(). Then it would be possible to modify
it later via /sys.

I am sorry for the noise.

Best Regards,
Petr