linux-kernel - Re: Regression due to 7ff9554 "printk: convert byte-buffer to variable-length record buffer"

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Message-ID: <4FAC2150.2060804@wwwdotorg.org>
Date:	Thu, 10 May 2012 14:13:04 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Kay Sievers <kay@...y.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	William Douglas <william.douglas@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-next@...r.kernel.org
Subject: Re: Regression due to 7ff9554 "printk: convert byte-buffer to variable-length
 record buffer"

On 05/10/2012 02:09 PM, Stephen Warren wrote:
> On 05/10/2012 02:06 PM, Kay Sievers wrote:
>> On Thu, May 10, 2012 at 9:54 PM, Stephen Warren <swarren@...dotorg.org> wrote:
>>> On 05/09/2012 12:31 PM, Stephen Warren wrote:
>>>> For me, next-20120508 prints nothing when booted, and I think also
>>>> hangs. To solve this, I reverted:
>>>>
>>>> 7ff9554 printk: convert byte-buffer to variable-length record buffer
>>>>
>>>> In order to build, I also had to revert:
>>>>
>>>> c4e00da driver-core: extend dev_printk() to pass structured data
>>>>
>>>> Note: I'm running on an ARM system using a serial console, with
>>>> earlyprintk enabled.
>>>
>>> This issue still occurs in next-20120510.
>>>
>>> I've tracked it down to the assignment of msg->ts_nsec near the end of
>>> log_store(). If I comment this out, everything works. The problem is the
>>> assignment, not the call to local_clock():
>>>
>>> fails:
>>>        msg->ts_nsec = local_clock();
>>> fails:
>>>        msg->ts_nsec = 0;//local_clock();
>>> works:
>>>        //msg->ts_nsec = local_clock();
>>
>> Weird.
>>
>> What happens if you change it to:
>>   cpu_clock(logbuf_cpu);
>> ?
>>
>> If it works, the timestamps look ok?
> 
> I doubt that would work - after all, assigning 0 fails, but not
> performing the assignment at all works. But, I'll go try it...

Calling cpu_clock() instead of local_clock() fails in the same way.
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