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Date:	Wed, 11 Nov 2009 13:35:22 +0900
From:	Jupyung Lee <>
To:	LKML <>
Cc:	Thomas Gleixner <>,
	Jupyung Lee <>
Subject: [PATCH-rt 1/1] softirqs: add preempt_check_resched() in ksoftirqd()

In its current preempt-rt kernel, ksoftirq() includes a series of primitives
related with kernel preemption and irq on/off, in the following order:

preempt_disable()		... (1)
local_irq_disable()		... (2)
__preempt_enable_no_resched()	... (3)
local_irq_enable()		... (4)

A problem arises if a process is awakened between (1) and (2) because
it is not given a chance to preempt the currently running process
for a while since (4): since (4), the kernel is preemptible, but there
is no explicit reschedule point.

A simple suggestion to resolve the problem is to add a reschedule point,
preempt_check_resched(), just after (4).

Signed-off-by: Jupyung Lee <>
 kernel/softirq.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 590049c..7c1b041 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -1037,6 +1037,7 @@ sleep_more:
 			set_softirq_pending(local_softirq_pending() & ~softirq_mask);
+			preempt_check_resched();
 			h = &softirq_vec[data->nr];
 			if (h)

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