netdev - Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT

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Date:	Thu, 14 Jan 2016 23:02:09 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>, netdev@...r.kernel.org
Subject: Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT

On 14.01.2016 15:50, Sebastian Andrzej Siewior wrote:
> * Thomas Gleixner | 2016-01-13 18:31:46 [+0100]:
>
>> On Wed, 13 Jan 2016, Sebastian Andrzej Siewior wrote:
>>> +#ifdef CONFIG_PREEMPT_RT_FULL
>>> +static inline int dev_recursion_level(void)
>>> +{
>>> +	return atomic_read(&current->xmit_recursion);
>>
>> Why would you need an atomic here. current does hardly race against itself.
>
> right.

We are just adding a second recursion limit solely to openvswitch which 
has the same problem:

https://patchwork.ozlabs.org/patch/566769/

This time also we depend on rcu_read_lock marking the section being 
nonpreemptible. Nice would be a more generic solution here which doesn't 
need to always add something to *current.

Thanks,
Hannes