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Subject: Re: [PATCH v4] kernel/signal: Signal-based pre-coredump notification
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        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>,
        Christian Brauner <christian@brauner.io>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        Rik van Riel <riel@surriel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Roman Gushchin <guro@fb.com>,
        Marcos Paulo de Souza <marcos.souza.org@gmail.com>,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
        "Victor Kamensky (kamensky)" <kamensky@cisco.com>,
        xe-linux-external@cisco.com, Stefan Strogin <sstrogin@cisco.com>,
        Enke Chen <enkechen@cisco.com>
References: <e7ed306f-8992-9d00-bcab-5131159e8d89@cisco.com>
 <458c04d8-d189-4a26-729a-bb1d1d751534@cisco.com>
 <7741efa7-a3f8-62a1-ba52-613883164643@cisco.com>
 <84460a77-a111-404e-4bad-88104a6e246e@cisco.com>
 <20181026082812.GA10581@redhat.com>
 <21f678a8-4001-df36-c26e-e96cf203b1b1@cisco.com>
 <20181029111804.GA24820@redhat.com>
From:   Enke Chen <enkechen@cisco.com>
Message-ID: <634f9518-c742-16f0-84f4-90943af6aed2@cisco.com>
Date:   Mon, 29 Oct 2018 14:08:34 -0700
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Hi, Oleg:

Yes, it should be the "real_parent" that is more interested in the notification.
Will revert back.

+static void do_notify_parent_predump(void)
+{
+	struct task_struct *parent;
+	int sig;
+
+	rcu_read_lock();
+	parent = rcu_dereference(current->real_parent);
+	sig = parent->signal->predump_signal;
+	if (sig != 0)
+		do_send_sig_info(sig, SEND_SIG_NOINFO, parent, PIDTYPE_TGID);
+	rcu_read_unlock();
+}

Thanks.  -- Enke

On 10/29/18 4:18 AM, Oleg Nesterov wrote:
> 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.
>