linux-kernel - Re: [PATCH] kdb: Change timespec to use timespec64

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Date:   Fri, 26 Jan 2018 09:40:10 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        kgdb-bugreport@...ts.sourceforge.net,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kdb: Change timespec to use timespec64

On 25 January 2018 at 23:12, Arnd Bergmann <arnd@...db.de> wrote:
> On Thu, Jan 25, 2018 at 3:49 PM, Jason Wessel
> <jason.wessel@...driver.com> wrote:
>> On 01/25/2018 05:38 AM, Daniel Thompson wrote:
>>>
>>> On Thu, Jan 25, 2018 at 05:18:54PM +0800, Baolin Wang wrote:
>>>>
>>>> On 25 January 2018 at 16:55, Arnd Bergmann <arnd@...db.de> wrote:
>>>>>
>>>>> On Thu, Jan 25, 2018 at 9:05 AM, Baolin Wang <baolin.wang@...aro.org>
>>>>> wrote:
>>>>>>
>>>>>> @@ -2554,7 +2554,7 @@ static int kdb_summary(int argc, const char
>>>>>> **argv)
>>>>>>          kdb_printf("domainname %s\n", init_uts_ns.name.domainname);
>>>>>>          kdb_printf("ccversion  %s\n", __stringify(CCVERSION));
>>>>>>
>>>>>> -       now = __current_kernel_time();
>>>>>> +       now = current_kernel_time64();
>>>>>>          kdb_gmtime(&now, &tm);
>>>>>>          kdb_printf("date       %04d-%02d-%02d %02d:%02d:%02d "
>>>>>>                     "tz_minuteswest %d\n",
>>>>>
>>>>>
>>>>> Thanks for picking this one up again, we should find a permanent
>>>>> solution here.
>>>>> Unfortunately you patch is incorrect, as we cannot safely call
>>>>> current_kernel_time64()
>>>>> from NMI context.
>>>>
>>>>
>>>> Ah, thanks for pointing out the issue, since I do not know what
>>>> context the function will be called in kdb.
>>>>
>>>>>
>>>>> The __ prefix on __current_kernel_time() indicates that this is a
>>>>> special call
>>>>> that intentionally doesn't read the hardware time to avoid taking locks
>>>>> that
>>>>> might already be held in the context from which we entered the debugger.
>>>>>
>>>>> See https://patchwork.kernel.org/patch/10002097/ for my earlier patch.
>>>>
>>>>
>>>> This patch had not been merged into mainline?
>>>
>>>
>>> Not yet (and I'm afraid it's not in kgdb-next either) but the ack from
>>> Jason is from
>>> this kernel cycle so we'll see what can be done!
>>>
>>>
>>
>> I thought for what ever reason this was going through the time keeper
>> subtree.   I added it immediately to kgdb-next so it will be evaluated in
>> the linux-next tree in the next day or so, and we can get this merged in the
>> merge window.
>
> Ok, thanks a lot!
>
> We should still come up with a patch for kdb_sysinfo(), which doesn't
> have a problem with time overflow (monotonic time doesn't overflow)
> but has an issue with locking and uses 'struct timespec'.
>
> Baolin, could you respin your patch on top of Jason's tree and
> replace ktime_get_ts64() with something based on ktime_get_fast_ns?

Sure, I will do that today.

-- 
Baolin.wang
Best Regards