On Fri, Dec 04, 2020 at 06:01:56PM +0100, Thomas Gleixner wrote:
> From: Thomas Gleixner <t...@linutronix.de>
>
> On RT a task which has soft interrupts disabled can block on a lock and
> schedule out to idle while soft interrupts are pending. This triggers the
> warning in the NOHZ idle code which complains about going idle with pending
> soft interrupts. But as the task is blocked soft interrupt processing is
> temporarily blocked as well which means that such a warning is a false
> positive.
>
> To prevent that check the per CPU state which indicates that a scheduled
> out task has soft interrupts disabled.
>
> Signed-off-by: Thomas Gleixner <t...@linutronix.de>
> ---
> include/linux/bottom_half.h | 6 ++++++
> kernel/softirq.c | 15 +++++++++++++++
> kernel/time/tick-sched.c | 2 +-
> 3 files changed, 22 insertions(+), 1 deletion(-)
>
> --- a/include/linux/bottom_half.h
> +++ b/include/linux/bottom_half.h
> @@ -32,4 +32,10 @@ static inline void local_bh_enable(void)
> __local_bh_enable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET);
> }
>
> +#ifdef CONFIG_PREEMPT_RT
> +extern bool local_bh_blocked(void);
> +#else
> +static inline bool local_bh_blocked(void) { return false; }
> +#endif
> +
> #endif /* _LINUX_BH_H */
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -138,6 +138,21 @@ static DEFINE_PER_CPU(struct softirq_ctr
> .lock = INIT_LOCAL_LOCK(softirq_ctrl.lock),
> };
>
> +/**
> + * local_bh_blocked() - Check for idle whether BH processing is blocked
> + *
> + * Returns false if the per CPU softirq::cnt is 0 otherwise true.
> + *
> + * This is invoked from the idle task to guard against false positive
> + * softirq pending warnings, which would happen when the task which holds
> + * softirq_ctrl::lock was the only running task on the CPU and blocks on
> + * some other lock.
> + */
> +bool local_bh_blocked(void)
> +{
> + return this_cpu_read(softirq_ctrl.cnt) != 0;
__this_cpu_read()
Reviewed-by: Frederic Weisbecker <frede...@kernel.org>
