linux-kernel - Re: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT

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Message-ID: <20250107115606.q67--i0f@linutronix.de>
Date: Tue, 7 Jan 2025 12:56:06 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Robert Joslyn <robert_joslyn@...inc.com>
Cc: linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	tglx@...utronix.de, rostedt@...dmis.org,
	Shrikanth Hegde <sshegde@...ux.ibm.com>
Subject: Re: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

On 2024-12-26 11:12:38 [-0800], Robert Joslyn wrote:
> This branch is needed to allow preemptible IRQs to be scheduled,
> otherwise the kernel hangs during boot on my e300 based platforms.
> This branch is needed for both CONFIG_PREEMPT and CONFIG_PREEMPT_RT,
> so broaden the check to CONFIG_PREEMPTION, which is selected by both.
> 
> This was previously set to CONFIG_PREEMPTION, but was reverted as part
> of removing LAZY_PREEMPT support.

I remember I pointed this out while Shrikanth posted the preempt-lazy
patches but didn't realize that I need this in RT tree, too.

The lazy-preempt patches for powerpc were merged upstream, I am going to
pull them into the v6.6-series.
I am going to Cc you, hopefully you can confirm that it is working.

> Fixes: b33022a48c79
> Signed-off-by: Robert Joslyn <robert_joslyn@...inc.com>
> ---
>  arch/powerpc/kernel/interrupt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index af62ec974b97..970039af8e92 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -396,7 +396,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
>  		/* Returning to a kernel context with local irqs enabled. */
>  		WARN_ON_ONCE(!(regs->msr & MSR_EE));
>  again:
> -		if (IS_ENABLED(CONFIG_PREEMPT)) {
> +		if (IS_ENABLED(CONFIG_PREEMPTION)) {
>  			/* Return to preemptible kernel context */
>  			if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
>  				if (preempt_count() == 0)

Sebastian