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Date: Thu, 2 Feb 2012 10:15:45 +0100 (CET)
From: Julia Lawall <julia.lawall@lip6.fr>
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To: Josh Triplett <josh@joshtriplett.org>
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        fweisbec@gmail.com, patches@linaro.org,
        "Paul E. McKenney" <paul.mckenney@linaro.org>,
        Julia Lawall <julia@diku.dk>
Subject: Re: [PATCH RFC tip/core/rcu 31/41] rcu: Add CPU-stall capability to
 rcutorture
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On Wed, 1 Feb 2012, Josh Triplett wrote:

> On Wed, Feb 01, 2012 at 11:41:49AM -0800, Paul E. McKenney wrote:
>> --- a/kernel/rcutorture.c
>> +++ b/kernel/rcutorture.c
>> +/* Spawn CPU-stall kthread, if stall_cpu specified. */
>> +static int __init rcu_torture_stall_init(void)
>> +{
>> +	if (stall_cpu <= 0)
>> +		return 0;
>> +	stall_task = kthread_run(rcu_torture_stall, NULL, "rcu_torture_stall");
>> +	if (IS_ERR(stall_task)) {
>> +		stall_task = NULL;
>> +		return PTR_ERR(stall_task);
>
> This seems...unlikely to produce the desired result. :)
>
> A quick check turns up the same bug in rcutorture_onoff_init.
>
> This suggests a possible Coccinelle check, for uses of PTR_ERR(foo) after
> foo = (any constant other than ERR_PTR(foo)).

Indeed, it seems to be a popular idiom :)  I'll send some patches later 
today.

julia