linux-kernel - Re: [PATCH v1 1/3] printk: honor the max_reason field in kmsg

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Date:   Mon, 4 May 2020 23:12:38 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     James Morris <jmorris@...ei.org>, Sasha Levin <sashal@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>, anton@...msg.org,
        ccross@...roid.com, Tony Luck <tony.luck@...el.com>,
        robh+dt@...nel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v1 1/3] printk: honor the max_reason field in kmsg_dumper

On Mon, May 4, 2020 at 10:52 PM Pavel Tatashin
<pasha.tatashin@...een.com> wrote:
>
> > > @@ -3157,12 +3162,9 @@ void kmsg_dump(enum kmsg_dump_reason reason)
> > >       struct kmsg_dumper *dumper;
> > >       unsigned long flags;
> > >
> > > -     if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)
> > > -             return;
> > > -
> > >       rcu_read_lock();
> > >       list_for_each_entry_rcu(dumper, &dump_list, list) {
> > > -             if (dumper->max_reason && reason > dumper->max_reason)
> > > +             if (reason > dumper->max_reason)
> > >                       continue;
> >
> > Why always_kmsg_dump check moved from the dumper loop entry point to the
> > dumper registration code? What if the user change always_ksmsg_dump
> > dynamically via sysfs?
>
> Hi Sergey,
>
> I changed it to make code cleaner:  for such basic operation there are
> too many conditions if we will keep it inside the kmsg_dump().
> However, if being able to set always_kmsg_dump dynamically during
> runtime is deemed important, I can change it back to be checked in
> kmsg_dump.

If you agree that we do not have to modify this variable dynamically,
I will also change the permission here:
module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);

>
> Thank you,
> Pasha
>
> >
> >         -ss