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Message-ID: <4b8ae129-45f9-33f9-673e-b134b4c36324@quicinc.com>
Date: Tue, 8 Feb 2022 19:10:22 +0530
From: Mukesh Ojha <quic_mojha@...cinc.com>
To: <linux-kernel@...r.kernel.org>
CC: <peterz@...radead.org>, <tglx@...utronix.de>, <paulmck@...nel.org>,
<will@...nel.org>, <dave@...olabs.net>, <frederic@...nel.org>
Subject: Re: [PATCH] softirq: Remove raise_softirq from
tasklet_action_common()
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@...cinc.com>
> ---
> 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();
> }
> }
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