Message-ID: <5553017A.2080905@linux.vnet.ibm.com>
Date: Wed, 13 May 2015 13:17:06 +0530
From: Shreyas B Prabhu <shreyas@linux.vnet.ibm.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.0
MIME-Version: 1.0
To: Steven Rostedt <rostedt@goodmis.org>,
        Andrew Morton <akpm@linux-foundation.org>
CC: linux-kernel@vger.kernel.org, mingo@redhat.com,
        aneesh.kumar@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com,
        preeti@linux.vnet.ibm.com, mgorman@suse.de, namhyung@kernel.org,
        lizf@cn.fujitsu.com, acme@redhat.com
Subject: Re: [PATCH RESEND 0/3] tracing/mm: Fix suspicious rcu_dereference_check()
 usage warnings
References: <1431105646-26558-1-git-send-email-shreyas@linux.vnet.ibm.com> <5551ABD6.9050007@linux.vnet.ibm.com> <20150512160351.4b5d5606@gandalf.local.home> <20150512133601.2f619efe74d08ed9281667d1@linux-foundation.org> <20150512165446.6daf5a4a@gandalf.local.home>
In-Reply-To: <20150512165446.6daf5a4a@gandalf.local.home>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1770
Lines: 56


On Wednesday 13 May 2015 02:24 AM, Steven Rostedt wrote:
> On Tue, 12 May 2015 13:36:01 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
>> On Tue, 12 May 2015 16:03:51 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
>>
>>> On Tue, 12 May 2015 12:59:26 +0530
>>> Shreyas B Prabhu <shreyas@linux.vnet.ibm.com> wrote:
>>>
>>>> Hi Steven,
>>>> On closer look, there is no particular maintainer who picks changes to
>>>> this file. Can you please pick these up?
>>>
>>> Perhaps Andrew Morton?
>>>
>>> No problem, I can take these too.
>>>
>>
>> I grabbed them, thanks.
>>

Thanks Andrew.

>>> +	TP_CONDITION(cpu_online(smp_processor_id())),
>>
>> Are we sure these can't generate check_preemption_disabled() warnings? 
>> Is there some reason why all these calls always occur with preemption
>> disabled?
> 
> Good catch. I don't think the code does.
> 
> Now, I'm not sure if we should just add a raw_smp_processor_id(). The
> idea is just to make sure that the CPU we are running on is online,
> because it is possible to call theses trace points when the CPU is
> going offline. If that happens, then there's a race with RCU.
> 
> Since a task can not be migrated to an offline CPU, we don't need to
> worry about the cpu_online(smp_processor_id()) returning a false
> positive. A false negative would just skip a tracepoint, but I'm not
> sure that is possible either.
> 
> In any case, comments should also be added to why the condition is
> there.
> 
I'll send a patch adding the comments.

Thanks,
Shreyas

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/