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Subject: Re: [PATCH v5] kernel/signal: Signal-based pre-coredump notification
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Oleg Nesterov <oleg@redhat.com>,
        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>,
        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>
 <0c197608-3b7e-ffd1-8943-801a60beb917@cisco.com>
 <20181030164628.GD7643@redhat.com>
 <20181121163711.2c00316784d221eb1750edb0@linux-foundation.org>
 <ae3b48ef-6bb0-2bc2-eca6-651fdb2dce37@cisco.com>
 <20181121173341.707a0a869bf16b85f09d75b5@linux-foundation.org>
From:   Enke Chen <enkechen@cisco.com>
Message-ID: <08366d06-9f47-b80e-3662-a84c5107be89@cisco.com>
Date:   Wed, 21 Nov 2018 20:57:31 -0800
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Hi, Andrew:

As suggested, I will post them as a patch series (with the same version v5):

    [PATCH v5 1/2] kernel/signal: Signal-based pre-coredump notification
    [PATCH v5 2/2] selftests/prctl: selftest for pre-coredump signal notification

I have a diff for the manpage as well. I guess that it should be submitted separately
from the code.

Thanks.  -- Enke

On 11/21/18 5:33 PM, Andrew Morton wrote:
> On Wed, 21 Nov 2018 17:09:50 -0800 Enke Chen <enkechen@cisco.com> wrote:
> 
>> Hi, Andrew:
>>
>> On 11/21/18 4:37 PM, Andrew Morton wrote:
>>> On Tue, 30 Oct 2018 17:46:29 +0100 Oleg Nesterov <oleg@redhat.com> wrote:
>>>
>>>> On 10/29, Enke Chen wrote:
>>>>>
>>>>> Reviewed-by: Oleg Nesterov <oleg@redhat.com>
>>>>
>>>> Hmm. I didn't say this ;)
>>>>
>>>> But OK, feel free to keep this tag.
>>>>
>>>> I do not like this feauture.
>>>
>>> Why is that?
>>>
>>>> But I see no technical problems in this version
>>>> and I never pretented I understand the user-space needs, so I won't argue.
>>>
>>> The changelog appears to spell this all out quite well?  Unusually
>>> well, in my experience ;)
>>
>> I also followed up with a little more explanation in the email thread on
>> 10/30/2018:
>>
>> ---
>> As I explained earlier, the primary application is in the area of network
>> high-availability / non-stop-forwarding where early fault notification and
>> early action can help maintain BFD sessions and thus avoid unnecessary
>> disruption to forwarding while the control-plane is recovering.
>> ---
>>
>> BTW, I probably should have pointed out this earlier:
>>
>> BFD stands for "RFC 5880: Bi-directional forwarding detection".
> 
> I saw that.  My point is that your above followup wasn't necessary -
> the changelog is clear!
> 
>>>
>>> - As it's a linux-specific feature, a test under
>>>   tools/testing/selftests would be appropriate.  I don't know how much
>>>   that work will be. 
>>
>> The selftest code was submitted on 10/25/2018:
>>
>>    [PATCH] selftests/prctl: selftest for pre-coredump signal notification
> 
> OK, please prepare these as a patch series.
> 
>>> Do we have other linux-specific signal extensions which could piggyback onto that?
>>
>> No. There are enough existing signals that an application can choose for this
>> purpose, such as SIGUSR1, SIGUSR1, and any of the RT signals.
>>
> 
> My point is that if we have previously added any linux-specific signal
> expensions then your selftest patch would be an appropriate place where
> we could add tests for those features.  I'm not saying that you should
> add such tests at this time, but please do prepare the selftest as a
> thing which tests linux-specific signal extensions in general, not as a
> thing which tests pre-coredump signals only.
>