linux-kernel - [PATCH] softirq: Remove raise_softirq from tasklet_action

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Message-ID: <1644066805-17212-1-git-send-email-quic_mojha@quicinc.com>
Date:   Sat, 5 Feb 2022 18:43:25 +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>,
        Mukesh Ojha <quic_mojha@...cinc.com>
Subject: [PATCH] softirq: Remove raise_softirq from tasklet_action_common()

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();
 	}
 }
-- 
2.7.4