linux-kernel - Re: [PATCH v5] kernel/signal: Signal-based pre-coredump notification

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Date:   Wed, 21 Nov 2018 20:57:31 -0800
From:   Enke Chen <enkechen@...co.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        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>,
        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>,
        Enke Chen <enkechen@...co.com>
Subject: Re: [PATCH v5] kernel/signal: Signal-based pre-coredump notification

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@...co.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@...hat.com> wrote:
>>>
>>>> On 10/29, Enke Chen wrote:
>>>>>
>>>>> Reviewed-by: Oleg Nesterov <oleg@...hat.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.
>