linux-kernel - Re: Hang on large copy_from_user with PREEMPT

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Date:	Tue, 07 Apr 2015 13:00:48 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Ingo Molnar <mingo@...nel.org>, Michal Hocko <mhocko@...e.cz>
CC:	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Dave Jones <davej@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: Hang on large copy_from_user with PREEMPT_NONE

On 04/07/2015 10:37 AM, Ingo Molnar wrote:
> 
> * Michal Hocko <mhocko@...e.cz> wrote:
> 
>> On Tue 07-04-15 13:05:31, Ingo Molnar wrote:
>>>
>>> * Borislav Petkov <bp@...en8.de> wrote:
>>>
>>>> On Tue, Apr 07, 2015 at 11:31:45AM +0200, Ingo Molnar wrote:
>>>>> Would be nice to see the actual kernel .config, as there's a few
>>>>> debug features that can slow things down significantly, such as
>>>>> CONFIG_KMEMCHECK=y or in some cases CONFIG_DEBUG_PAGEALLOC=y.
>>>>
>>>> He sent it here: https://lkml.kernel.org/r/55229D7E.6080309@oracle.com
>>>>
>>>> I'm attaching it again.
>>>
>>> Thanks. Nothing particularly expensive stands out to me at a quick 
>>> glance:-/
>>
>> Sasha uses KASAN very often and it is enabled here as well. I guess 
>> this might slow things really down.
> 
> Indeed, that kind of instrumentation might explain the overhead ...

It locks up quickly without KASan as well.


Thanks,
Sasha

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