linux-kernel - Re: [PATCH] efi: cper: avoid using get

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Message-ID: <CAKv+Gu9zYJk+ubcn8ngqsXPBbxWM-S5kUWAHfe_zKDm1=FWB4w@mail.gmail.com>
Date:   Mon, 18 Jun 2018 17:56:48 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     y2038 Mailman List <y2038@...ts.linaro.org>,
        Tyler Baicar <tbaicar@...eaurora.org>,
        Will Deacon <will.deacon@....com>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        gengdongjiu <gengdongjiu@...wei.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] efi: cper: avoid using get_seconds()

On 18 June 2018 at 17:54, Arnd Bergmann <arnd@...db.de> wrote:
> On Mon, Jun 18, 2018 at 5:50 PM, Ard Biesheuvel
> <ard.biesheuvel@...aro.org> wrote:
>> On 18 June 2018 at 17:49, Arnd Bergmann <arnd@...db.de> wrote:
>>> On Mon, Jun 18, 2018 at 5:47 PM, Ard Biesheuvel
>>> <ard.biesheuvel@...aro.org> wrote:
>>>> On 18 June 2018 at 16:17, Arnd Bergmann <arnd@...db.de> wrote:
>>>
>>>>> -               atomic64_set(&seq, ((u64)get_seconds()) << 32);
>>>>> +       if (!atomic64_read(&seq)) {
>>>>> +               time64_t time = ktime_get_real_seconds();
>>>>> +
>>>>> +               /*
>>>>> +                * This code is unlikely to still be needed in year 2106,
>>>>> +                * but just in case, let's use a few more bits for timestamps
>>>>> +                * after y2038 to be sure they keep increasing monotonically
>>>>> +                * for the next few hundred years...
>>>>> +                */
>>>>> +               if (time < 0x80000000)
>>>>> +                       atomic64_set(&seq, (ktime_get_real_seconds()) << 32);
>>>>> +               else
>>>>> +                       atomic64_set(&seq, 0x8000000000000000ull |
>>>>> +                                          ktime_get_real_seconds() << 24);
>>>>> +       }
>>>>
>>>> Given that these values are never decoded and interpreted as
>>>> timestamps, can't we simply switch to the second flavour immediately?
>>>
>>> I considered that, but the downside would be that all future filenames would
>>> come before all past file names.
>>
>> Won't we have that same problem in 2038?
>
> No, it goes from 0x7fffffff00000000 to 0x8000000000000000, followed
> by 0x8000000001000000.
>

Ah, right. I'm with you now :-)

I'll queue this in the efi tree.