linux-kernel - Re: [PATCH] print_worker_info: Handle pointer with more care

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Message-ID: <520E500B.5000408@nod.at>
Date:	Fri, 16 Aug 2013 18:15:07 +0200
From:	Richard Weinberger <richard@....at>
To:	Tejun Heo <tj@...nel.org>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] print_worker_info: Handle pointer with more care

Am 16.08.2013 18:12, schrieb Tejun Heo:
> On Fri, Aug 16, 2013 at 05:56:46PM +0200, Richard Weinberger wrote:
>> The function has a nice comment:
>> /*
>>  * This function is called without any synchronization and @task
>>  * could be in any state.  Be careful with dereferences.
>>  */
>>
>> But a few lines later it blindly dereferences a few pointers.
>> E.g. It can happen that the worker function is already done,
>> then worker->current_pwq is NULL.
> ...
>>  	probe_kernel_read(&fn, &worker->current_func, sizeof(fn));
>>  	probe_kernel_read(&pwq, &worker->current_pwq, sizeof(pwq));
>> +	if (!pwq)
>> +		goto print;
>> +
>>  	probe_kernel_read(&wq, &pwq->wq, sizeof(wq));
>> +	if (!wq)
>> +		goto print;
>> +
> 
> But none of the above are dereferences.  &ptr->field is offset
> calculation, not a dereference.

On UML I hit the case that pwq is NULL.
Then we oops at &pwq->wq...

Thanks,
//richard

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