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

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Message-ID: <4FAC2304.7050705@wwwdotorg.org>
Date:	Thu, 10 May 2012 14:20:20 -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 02:15 PM, Kay Sievers wrote:
> On Thu, May 10, 2012 at 10:13 PM, Stephen Warren <swarren@...dotorg.org> wrote:
>> 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.
> 
> Ok, didn't really see the assign to 0 you tried, sorry. :)
> 
> And 'dmesg' works when you run the box with the line commented out?
> 
> And 'cat /dev/kmsg'?

Yes, both work and produce reasonable output. "cat /dev/kmsg" does hang
at the end of the log until I CTRL-C it - is that expected?
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