On Thu, 13 Aug 2020 03:03:46 +0000
Jiafei Pan <jiafei....@nxp.com> wrote:
> Any comments? Thanks.
>
> @Steven Rostedt, I thinks irq off checking is necessary especially
> This is probably more for Thomas Gleixner.
Thanks Steven.
@Thomas Gleixner, would you please review the patch? thanks.
Jiafei.
> for Preempt-RT kernel, because some context may be changed from irq
> off to irq on when enable Preempt RT, I once met a issue that hrtimer
> soft irq is lost when enabled Preempt RT, finally I found
> napi_schedule_irqoff is called in hardware interrupt handler, there
> maybe no issue for non RT kernel, but for Preempt RT, interrupt is
> threaded, so irq is on in interrupt handler, the result is
> __raise_softirq_irqoff is called in irq on context, so that per-CPU
> softirq masking is corrupted because of the process of updating of
> soft irq masking is interrupted and not a atomic operation , and then
> caused hrtimer soft irq is lost. So I think adding irq status checking
> in __raise_softirq_irqoff can report such issue directly and help us
> to find the root cause of such issue.
>
> I know that there may be performance impaction to add extra checking
> here, if it is the case, how about to include it in some debug
> configuration items? Such as CONFIG_DEBUG_PREEMPT or other debug
> items?
>
> Best Regards,
> Jiafei.
>
> -----Original Message-----
> From: Jiafei Pan <jiafei....@nxp.com>
> Sent: Thursday, August 6, 2020 12:07 PM
> To: pet...@infradead.org; mi...@kernel.org; t...@linutronix.de;
> rost...@goodmis.org; romain.per...@gmail.com; w...@kernel.org
> Cc: linux-kernel@vger.kernel.org; linux-rt-us...@vger.kernel.org;
> Jiafei Pan <jiafei....@nxp.com>; Leo Li <leoyang...@nxp.com>; Vladimir
> Oltean <vladimir.olt...@nxp.com>; Jiafei Pan <jiafei....@nxp.com>
> Subject: [PATCH] softirq: add irq off checking for
> __raise_softirq_irqoff
>
> __raise_softirq_irqoff will update per-CPU mask of pending softirqs, it need
> to be called in irq disabled context in order to keep it atomic operation,
> otherwise it will be interrupted by hardware interrupt, and per-CPU softirqs
> pending mask will be corrupted, the result is there will be unexpected issue,
> for example hrtimer soft irq will be losed and soft hrtimer will never be
> expire and handled.
Please wrap your change logs.
>
> Adding irqs disabled checking here to provide warning in irqs enabled context.
>
> Signed-off-by: Jiafei Pan <jiafei....@nxp.com>
> ---
> kernel/softirq.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/softirq.c b/kernel/softirq.c index
> bf88d7f62433..11f61e54a3ae 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -481,6 +481,11 @@ void raise_softirq(unsigned int nr)
>
> void __raise_softirq_irqoff(unsigned int nr) {
> + /* This function can only be called in irq disabled context,
> + * otherwise or_softirq_pending will be interrupted by hardware
> + * interrupt, so that there will be unexpected issue.
> + */
> + WARN_ON_ONCE(!irqs_disabled());
Perhaps: lockdep_assert_irqs_disabled() is more appropriate, and doesn't add
extra overhead on production systems.
-- Steve
> trace_softirq_raise(nr);
> or_softirq_pending(1UL << nr);
> }
> --
> 2.17.1
