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Date: Wed, 11 Nov 2009 08:21:28 +0100 (CET)
From: Thomas Gleixner <tglx@...utronix.de>
To: Jupyung Lee <jupyung@...il.com>
cc: LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH-rt 1/1] softirqs: add preempt_check_resched() in
ksoftirqd()
Jupyung,
On Wed, 11 Nov 2009, Jupyung Lee wrote:
> 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).
Good catch. I applied it with a simple modification.
Thanks,
tglx
---
commit ca0b4bfa5994856bbcf4227e29f9c73722efaef2
Author: Jupyung Lee <jupyung@...il.com>
<snip>
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -1033,10 +1033,10 @@ sleep_more:
goto sleep_more;
}
per_cpu(softirq_running, cpu) |= softirq_mask;
- __preempt_enable_no_resched();
set_softirq_pending(local_softirq_pending() & ~softirq_mask);
local_bh_disable();
local_irq_enable();
+ preempt_enable();
h = &softirq_vec[data->nr];
if (h)
--
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