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Date:   Mon, 29 Oct 2018 12:18:05 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Enke Chen <enkechen@cisco.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
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        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Khalid Aziz <khalid.aziz@oracle.com>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        Helge Deller <deller@gmx.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
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        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        Rik van Riel <riel@surriel.com>,
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        Kees Cook <keescook@chromium.org>, x86@kernel.org,
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        "Victor Kamensky (kamensky)" <kamensky@cisco.com>,
        xe-linux-external@cisco.com, Stefan Strogin <sstrogin@cisco.com>
Subject: Re: [PATCH v4] kernel/signal: Signal-based pre-coredump notification
Message-ID: <20181029111804.GA24820@redhat.com>
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Hi,

On 10/26, Enke Chen wrote:
>
> This is really a good idea given that "parent" is declared as RCU-protected.
> Just a bit odd, though, that the "parent" has not been accessed this way in
> the code base.

It is acccessed when possible,

> So just to confirm: the revised code would look like the following:
>
> static void do_notify_parent_predump(void)
> {
>         struct task_struct *parent;
>         int sig;
>
>         rcu_read_lock();
>         parent = rcu_dereference(current->parent);
>         sig = parent->signal->predump_signal;
>         if (sig != 0)
>                 do_send_sig_info(sig, SEND_SIG_NOINFO, parent, PIDTYPE_TGID);
>         rcu_read_unlock();
> }

Yes, this is what I meant.

But I still think do_notify_parent_predump() should notify ->real_parent,
not ->parent.

Oleg.