linux-kernel - [PATCH] Delete redundant IRQ_DISABLED check in irq

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Date:	Fri, 17 Jul 2009 16:43:49 +0800
From:	Barry Song <21cnbao@...il.com>
To:	mingo@...hat.com, dahlmann.thomas@...or.de
CC:	linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org,
	Barry Song <21cnbao@...il.com>
Subject: [PATCH] Delete redundant IRQ_DISABLED check in irq_thread

Signed-off-by: Barry Song <21cnbao@...il.com>
I think it is completely redundant to check IRQ_DISABLED to decide whether thread_fn will be called.

At first, the irq_thread is waken up by HARDIRQ handler, if IRQ_DISABLED is true, HARDIRQ will have no chance to run, then irq_thread will not run. So there is only a situation that both HARDIRQ can run and IRQ_DISABLED is set.
The case is that the flag is set in the interval of HARDIRQ enter and irq_thread is scheduled to run. I think there is nobody which is interested to disable irq in the interval except HARDIRQ handler itself. Then that causes the second problem I will explain.

Secondly, checking the flag causes some problems in fact. We often call disable_irq_nosync to diable irq in HARDIRQ to avoid flooding irq to follow. But the disable_irq_nosync will set IRQ_DISABLED flag, then that will prevent the execution of thread_fn. That's not the original idea to call disable_irq_nosync in HARDIRQ.

So I guess deleting the check is maybe better and more compact.

-Barry
---
 kernel/irq/manage.c |   17 +----------------
 1 files changed, 1 insertions(+), 16 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 50da676..ff4e05d 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -460,22 +460,7 @@ static int irq_thread(void *data)

 		atomic_inc(&desc->threads_active);

-		spin_lock_irq(&desc->lock);
-		if (unlikely(desc->status & IRQ_DISABLED)) {
-			/*
-			 * CHECKME: We might need a dedicated
-			 * IRQ_THREAD_PENDING flag here, which
-			 * retriggers the thread in check_irq_resend()
-			 * but AFAICT IRQ_PENDING should be fine as it
-			 * retriggers the interrupt itself --- tglx
-			 */
-			desc->status |= IRQ_PENDING;
-			spin_unlock_irq(&desc->lock);
-		} else {
-			spin_unlock_irq(&desc->lock);
-
-			action->thread_fn(action->irq, action->dev_id);
-		}
+		action->thread_fn(action->irq, action->dev_id);

 		wake = atomic_dec_and_test(&desc->threads_active);

-- 
1.5.6.3

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