Re: [PATCH] rcutorture: Avoid problematic critical section nesting on RT

[Sebastian Andrzej Siewior]

On 2021-08-19 22:23:37 [-0500], Scott Wood wrote:
> On Tue, 2021-08-17 at 16:40 +0200, Sebastian Andrzej Siewior wrote:
> > [bigeasy: remove 'preempt_disable(); local_bh_disable(); preempt_enable();
> >  local_bh_enable();' from the examples because this works on RT now. ]
> 
> Does it actually work?  If preemption is disabled during local_bh_disable,
> softirq_ctrl.lock won't be taken.  If you then get preempted between the
> preempt_enable() and the local_bh_enable(), and another task tries to do
> local_bh_disable(), won't it successfully get softirq_ctrl.lock, add to
> softirq_ctrl.cnt, and proceed right into the critical section?
> 
> Or am I missing something?

No, I mixed it up with migrate_disable/enable. I corrected it while
redoing it yesterday.

> -Scott

Sebastian