linux-kernel - [PATCH] rcu: remove the context test in rcu_read_unlock

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Message-ID: <4F741B98.2070709@cn.fujitsu.com>
Date:	Thu, 29 Mar 2012 16:21:44 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] rcu: remove the context test in rcu_read_unlock_special()

Because of commit#26861f and #10f39bb1b2, the context test in
rcu_read_unlock_special() are not needed.

commit#26861f and #10f39bb1b2 ensure ->rcu_read_unlock_special is zero
after rcu_read_unlock(), which implies:

if ->rcu_read_unlock_special is non-zero, the out-most RCU C.S. can
be interrupted or can be preempted, such context is safe to
call rcu_read_unlock_special().

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 22ecea0..22e2ef1 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -571,12 +571,6 @@ static noinline void rcu_read_unlock_special(struct task_struct *t)
 	if (special & RCU_READ_UNLOCK_NEED_QS)
 		rcu_preempt_cpu_qs();
 
-	/* Hardware IRQ handlers cannot block. */
-	if (in_irq() || in_serving_softirq()) {
-		local_irq_restore(flags);
-		return;
-	}
-
 	/* Clean up if blocked during RCU read-side critical section. */
 	if (special & RCU_READ_UNLOCK_BLOCKED) {
 		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index c023464..2bd3689 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -338,12 +338,6 @@ static noinline void rcu_read_unlock_special(struct task_struct *t)
 		rcu_preempt_qs(smp_processor_id());
 	}
 
-	/* Hardware IRQ handlers cannot block. */
-	if (in_irq() || in_serving_softirq()) {
-		local_irq_restore(flags);
-		return;
-	}
-
 	/* Clean up if blocked during RCU read-side critical section. */
 	if (special & RCU_READ_UNLOCK_BLOCKED) {
 		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 671f959..7074f97 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -318,12 +318,8 @@ static inline void invoke_softirq(void)
 #else
 		do_softirq();
 #endif
-	} else {
-		__local_bh_disable((unsigned long)__builtin_return_address(0),
-				SOFTIRQ_OFFSET);
+	} else
 		wakeup_softirqd();
-		__local_bh_enable(SOFTIRQ_OFFSET);
-	}
 }
 
 /*
--
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