linux-kernel - Re: [PATCH v4] kernel/signal: Signal-based pre-coredump notification

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Message-ID: <20181029111804.GA24820@redhat.com>
Date:   Mon, 29 Oct 2018 12:18:05 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Enke Chen <enkechen@...co.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Helge Deller <deller@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian@...uner.io>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Dave Martin <Dave.Martin@....com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Roman Gushchin <guro@...com>,
        Marcos Paulo de Souza <marcos.souza.org@...il.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        "Victor Kamensky (kamensky)" <kamensky@...co.com>,
        xe-linux-external@...co.com, Stefan Strogin <sstrogin@...co.com>
Subject: Re: [PATCH v4] kernel/signal: Signal-based pre-coredump notification

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.