linux-kernel - Re: [linux-next][regression] [PATCH] percpu: add preemption checks to __this

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Message-ID: <53297D1C.3000100@ti.com>
Date:	Wed, 19 Mar 2014 13:18:52 +0200
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>
CC:	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	Tejun Heo <tj@...nel.org>, <linux-kernel@...r.kernel.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [linux-next][regression] [PATCH] percpu: add preemption checks
 to __this_cpu ops

On 03/18/2014 11:37 PM, Andrew Morton wrote:> On Tue, 18 Mar 2014 10:54:06 -0500 (CDT) Christoph Lameter <cl@...ux.com> wrote:
> 
>> On Tue, 18 Mar 2014, Grygorii Strashko wrote:
>>
>>> Any way, I can boot and console works fine with your change :)
>>> Thanks.
>>
>> Ok here is the properly formatted patch:
>>
>>
>> Subject: preemption_checks: Avoid snprintf before checking error conditions
>>
>> snprintf can cause hangs.
> 
> This is weird.  How the heck can snprintf() fail if called too early?
> All it does is shuffle chars around in memory.  The only external
> dependency I'm seeing is a WARN_ON() which presumably didn't trigger
> anyway.
> 
> I'm suspecting a misdiagnosis here.  Otherwise, we seriously need to
> fix snprintf(), not work around it!

Not sure I can run debugger fast :(, but I'll try.

> 
> Also, what does "before checking error conditions" refer to?  Does this
> mean you know why snprintf() failed??

Just an assumption, May be the problem here not in snprintf, but in stack.
Looks like if I reduce stack usage the issue is gone:
char text[10];

> 
>> Move the string processing into the function
>> so that the string operations only occur when necessary after the
>> conditions have been checked.
>>
>> Tested-by: Grygorii Strashko <grygorii.strashko@...com>
> 
> Grygorii, thanks for testing linux-next on unusual machines - it's most
> helpful.
> 

Regards,
-grygorii
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