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Date:   Thu, 11 May 2023 17:52:19 +0800
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Subject: Re: [RFD] posix-timers: CRIU woes
Content-Language: en-US
To:     Thomas Gleixner <tglx@linutronix.de>,
        Andrey Vagin <avagin@openvz.org>
Cc:     Frederic Weisbecker <frederic@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Anna-Maria Behnsen <anna-maria@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        syzbot+5c54bd3eb218bb595aa9@syzkaller.appspotmail.com,
        Dmitry Vyukov <dvyukov@google.com>,
        Sebastian Siewior <bigeasy@linutronix.de>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Christian Brauner <brauner@kernel.org>,
        Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>,
        Pavel Emelyanov <xemul@openvz.org>
References: <20230425181827.219128101@linutronix.de>
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From:   Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
In-Reply-To: <87r0rnciqo.ffs@tglx>
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On 11.05.2023 17:36, Thomas Gleixner wrote:
> On Thu, May 11 2023 at 11:17, Pavel Tikhomirov wrote:
>> On 10.05.2023 16:16, Andrey Vagin wrote:
>>>>
>>>> So because of that half thought out user space ABI we are now up the
>>>> regression creek without a paddle, unless CRIU can accomodate to a
>>>> different restore mechanism to lift this restriction from the kernel.
>>>>
>>> If you give us a new API to create timers with specified id-s, we will
>>> figure out how to live with it. It isn't good to ask users to update
>>> CRIU to work on new kernels, but here are reasons and event improvements
>>> for CRIU, so I think it's worth it.
>>
>> I agree, any API to create timers with specified id-s would work for new
>> CRIU versions.
> 
> The real question is whether this will cause any upheaval when a new
> kernel meets a non-updated CRIU stack.

Creation of posix timer would hang forever in this loop 
https://github.com/checkpoint-restore/criu/blob/33dd66c6fc93c47213aaa0447a94d97ba1fa56ba/criu/pie/restorer.c#L1185 
if old criu is run on new kernel (without consecutive id allocation) AFAICS.

> You know the UABI regression rules of the kernel...
> 
> Thanks,
> 
>          tglx
> 

-- 
Best regards, Tikhomirov Pavel
Senior Software Developer, Virtuozzo.