linux-kernel - Re: Regression on cpufreq in v3.12-rc1

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Message-ID: <523AF50E.1040502@linux.vnet.ibm.com>
Date:	Thu, 19 Sep 2013 18:28:54 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: Regression on cpufreq in v3.12-rc1

On 09/19/2013 06:25 PM, Linus Walleij wrote:
> On Thu, Sep 19, 2013 at 2:46 PM, Srivatsa S. Bhat
> <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
> 
>>>> I don't really know if this is the right solution at all, so please
>>>> help me out here... if you want that patch I can send it once
>>>> I understand this properly.
>>
>> IIRC, recent kernels didn't return 0 or any error code when the !policy
>> condition was matched. So can you check whether this problem occurs with
>> 3.11 or 3.10 as well?
> 
> v3.11 works fine.
> 
> The problem is not what it returns, the system seems to survive no matter
> whether it returns 0 or 17 or whatever.
> 

Of course. What I intended to say was that I don't recall recent kernels
returning _anything_ on !policy. So there wasn't any sudden change in _that_
piece of code, AFAIR.

> The problem is that sometimes in the v3.12 kernel cycle we got a
> BUG() crash instead of some random value back for calling early.
> 

Yep, and that's most likely due to some change in ordering of calls somewhere,
which makes calls to lock_policy_rwsem_read() before it is safe to do so,
rather than anything related to how lock_policy_rwsem_read() handles the call.

>> So I think we should first identify (bisect?) and understand what caused that
>> particular change and then we will be in a position to evaluate whether the
>> patch you proposed would be the right fix or not.
> 
> I'll see if I can get a bisect going, the problem is that I upload the
> kernel over the serial port so this isn't a very quick procedure :-(
> 

Hmmm.. :-/

Regards,
Srivatsa S. Bhat

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