linux-kernel - Re: [PATCH] core_pattern: add CPU specifier

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Date:   Sun, 4 Sep 2022 21:38:44 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Oleksandr Natalenko <oleksandr@...hat.com>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Huang Ying <ying.huang@...el.com>,
        "Jason A . Donenfeld" <Jason@...c4.com>,
        Will Deacon <will@...nel.org>,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Stephen Kitt <steve@....org>, Rob Herring <robh@...nel.org>,
        Joel Savitz <jsavitz@...hat.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Xiaoming Ni <nixiaoming@...wei.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Renaud Métrich <rmetrich@...hat.com>,
        Grzegorz Halat <ghalat@...hat.com>, Qi Guo <qguo@...hat.com>
Subject: Re: [PATCH] core_pattern: add CPU specifier

On 09/04, Andrew Morton wrote:
>
> On Sat,  3 Sep 2022 08:43:30 +0200 Oleksandr Natalenko <oleksandr@...hat.com> wrote:
>
> > @@ -535,6 +539,7 @@ void do_coredump(const kernel_siginfo_t *siginfo)
> >  		 */
> >  		.mm_flags = mm->flags,
> >  		.vma_meta = NULL,
> > +		.cpu = raw_smp_processor_id(),
> >  	};
>
> Why use the "raw_" function here?

To avoid check_preemption_disabled() from debug_smp_processor_id().

We do not disable preemption because this is pointless, this is the
"racy snapshot" anyway. The coredumping task can migrate to another
CPU even before get_signal/do_coredump, right after exit-to-user
path enables irqs.

Oleg.