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Date:   Sun, 4 Sep 2022 21:38:44 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Oleksandr Natalenko <oleksandr@redhat.com>,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Huang Ying <ying.huang@intel.com>,
        "Jason A . Donenfeld" <Jason@zx2c4.com>,
        Will Deacon <will@kernel.org>,
        "Guilherme G . Piccoli" <gpiccoli@igalia.com>,
        Laurent Dufour <ldufour@linux.ibm.com>,
        Stephen Kitt <steve@sk2.org>, Rob Herring <robh@kernel.org>,
        Joel Savitz <jsavitz@redhat.com>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>,
        Xiaoming Ni <nixiaoming@huawei.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Renaud =?iso-8859-1?Q?M=E9trich?= <rmetrich@redhat.com>,
        Grzegorz Halat <ghalat@redhat.com>, Qi Guo <qguo@redhat.com>
Subject: Re: [PATCH] core_pattern: add CPU specifier
Message-ID: <20220904193844.GA7953@redhat.com>
References: <20220903064330.20772-1-oleksandr@redhat.com>
 <20220904112718.b7feead47012600ef255dfdf@linux-foundation.org>
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On 09/04, Andrew Morton wrote:
>
> On Sat,  3 Sep 2022 08:43:30 +0200 Oleksandr Natalenko <oleksandr@redhat.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.