Re: [PATCH] softirq: Remove raise_softirq from tasklet_action_common()

[Mukesh Ojha]

Hi All,

Sorry for the reminder so quickly as we are hitting this issue more 
frequently.
Please suggest if whether below patch will have any side-effect.

-Mukesh

On 2/5/2022 6:43 PM, Mukesh Ojha wrote:
> Think about a scenario when all other cores are in suspend
> and one core is only running ksoftirqd and it is because
> some client has invoked tasklet_hi_schedule() only once
> during that phase.
>
> tasklet_action_common() handles that softirq and marks the
> same softirq as pending again. And due to that core keeps
> running the softirq handler [1] forever and it is not able to
> go to suspend.
>
> We can get rid of raising softirq from tasklet handler.
>
> [1]
> <idle>-0    [003]   13058.769081:  softirq_entry   vec=0  action=HI_SOFTIRQ
> <idle>-0     [003]  13058.769085: softirq_raise:        vec=0 [action=HI_SOFTIRQ]
> <idle>-0    [003]   13058.769087:  softirq_exit   vec=0  action=HI_SOFTIRQ
> <idle>-0    [003]   13058.769091:  softirq_entry   vec=0  action=HI_SOFTIRQ
> <idle>-0     [003]  13058.769094: softirq_raise:        vec=0 [action=HI_SOFTIRQ]
> <idle>-0    [003]   13058.769097:  softirq_exit   vec=0  action=HI_SOFTIRQ
> <idle>-0    [003]   13058.769100:  softirq_entry   vec=0  action=HI_SOFTIRQ
> <idle>-0     [003]  13058.769103: softirq_raise:        vec=0 [action=HI_SOFTIRQ]
> <idle>-0    [003]   13058.769106:  softirq_exit   vec=0  action=HI_SOFTIRQ
> <idle>-0    [003]   13058.769109:  softirq_entry   vec=0  action=HI_SOFTIRQ
> <idle>-0    [003]   13059.058923:  softirq_entry   vec=0  action=HI_SOFTIRQ
> ...
> ..
> ..
> ..
>
> <idle>-0    [003]   13059.058951:  softirq_entry   vec=0  action=HI_SOFTIRQ
> <idle>-0     [003]  13059.058954: softirq_raise:        vec=0 [action=HI_SOFTIRQ]
> <idle>-0    [003]   13059.058957:  softirq_exit   vec=0  action=HI_SOFTIRQ
> <idle>-0    [003]   13059.058960:  softirq_entry   vec=0  action=HI_SOFTIRQ
> <idle>-0     [003]  13059.058963: softirq_raise:        vec=0 [action=HI_SOFTIRQ]
> <idle>-0    [003]   13059.058966:  softirq_exit   vec=0  action=HI_SOFTIRQ
> <idle>-0    [003]   13059.058969:  softirq_entry   vec=0  action=HI_SOFTIRQ
> <idle>-0     [003]  13059.058972: softirq_raise:        vec=0 [action=HI_SOFTIRQ]
> <idle>-0    [003]   13059.058975:  softirq_exit   vec=0  action=HI_SOFTIRQ
> <idle>-0    [003]   13059.058978:  softirq_entry   vec=0  action=HI_SOFTIRQ
> <idle>-0     [003]  13059.058981: softirq_raise:        vec=0 [action=HI_SOFTIRQ]
> <idle>-0    [003]   13059.058984:  softirq_exit   vec=0  action=HI_SOFTIRQ
> <idle>-0    [003]   13059.058987:  softirq_entry   vec=0  action=HI_SOFTIRQ
> <idle>-0     [003]  13059.058990: softirq_raise:        vec=0 [action=HI_SOFTIRQ]
> <idle>-0    [003]   13059.058993:  softirq_exit   vec=0  action=HI_SOFTIRQ
> <idle>-0    [003]   13059.058996:  softirq_entry   vec=0  action=HI_SOFTIRQ
> <idle>-0     [003]  13059.059000: softirq_raise:        vec=0 [action=HI_SOFTIRQ]
> <idle>-0    [003]   13059.059002:  softirq_exit   vec=0  action=HI_SOFTIRQ
>
> Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> ---
>   kernel/softirq.c | 1 -
>   1 file changed, 1 deletion(-)
>
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 41f4709..d3e6fb9 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -795,7 +795,6 @@ static void tasklet_action_common(struct softirq_action *a,
>   		t->next = NULL;
>   		*tl_head->tail = t;
>   		tl_head->tail = &t->next;
> -		__raise_softirq_irqoff(softirq_nr);
>   		local_irq_enable();
>   	}
>   }