Re: [ANNOUNCE] v5.14-rc4-rt4

On 2021-08-04 12:47:55 [-0400], Steven Rostedt wrote:

On Wed, 4 Aug 2021 18:31:19 +0200
Sebastian Andrzej Siewior [off-list ref] wrote:

quoted

CPU-local wake-ups just set NEED_RESCHED and wait for preempt_enable()
to do the magic. Just because the code not perform wake_up() now does
not mean it will not do so in the future. Also it is here as an example
which might be copied somewhere else.

Does this mean all local_irq_disable/enable() is audited? What do you do for;

	local_irq_disable();
	[..]
	wakeup_process(x); /* on local CPU */
	[..]
	local_irq_enable();

I hunted and fixed a few of those. I still have few
preempt_check_resched_rt() which I want fix other than what is in RT.

And if local_irq_disable() is not used anymore, or seldom, what harm
would it be to add a preemption check to that caller? And change
local_irq_enable() that is used internally by other atom functions be
called __local_irq_enable()?

Not to mention that we could just open code that too:

	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
		local_irq_enable();
		preempt_check_resched();
	}

And make it ugly enough that nobody will want to copy it :-)

I remember that the amount of enthusiasm was quite low when it was
suggested that local_irq_enable() gets additionally the preempt-check.
Maybe was due to the people involved :)
But we managed to work around it for most callers. Therefore we I
wouldn't suggest local_irq_disable_rt(). We had it in -RT, we had a
bunch of users and all of them were fixed in a different way.

Same goes btw. for preempt_disable_rt() which has been reduced to vmstat
and had previously more users :)

-- Steve

Sebastian