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Date:   Mon, 24 Apr 2023 16:34:38 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     Wander Lairson Costa <wander@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
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Subject: Re: [PATCH v6 2/3] sched/task: Add the
 put_task_struct_atomic_safe() function
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On Mon, 24 Apr 2023 11:52:52 -0700
"Paul E. McKenney" <paulmck@kernel.org> wrote:

> > softirqs execute in thread context in PREEMPT_RT. We are good here.  
> 
> So the sleeping lock is a spinlock rather than (say) a mutex?

local_bh_disable() on RT basically turns into:

	local_lock(&softirq_ctrl.lock);
	rcu_read_lock();

Which grabs a per CPU mutex that is taken by softirqs, and also calls
rcu_read_lock(). This allows bottom halves to still run as threads but
maintain the same synchronization as they do on mainline.

-- Steve