[PATCH 1/2] irq: Remove IRQ_EXIT_OFFSET workaround

[PATCH 1/2] irq: Remove IRQ_EXIT_OFFSET workaround

[Frederic Weisbecker]

The IRQ_EXIT_OFFSET trick was used to make sure the irq
doesn't get preempted after we substract the HARDIRQ_OFFSET
until we are entirely done with any code in irq_exit().

This workaround was necessary because some archs may call
irq_exit() with irqs enabled and there is still some code
in the end of this function that is not covered by the
HARDIRQ_OFFSET but want to stay non-preemptible.

Now that irq are always disabled in irq_exit(), the whole code
is guaranteed not to be preempted. We can thus remove this hack.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/hardirq.h |    2 --
 kernel/softirq.c        |    3 +--
 2 files changed, 1 insertions(+), 4 deletions(-)

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 29eb805..c1d6555 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -118,10 +118,8 @@
 
 #ifdef CONFIG_PREEMPT_COUNT
 # define preemptible()	(preempt_count() == 0 && !irqs_disabled())
-# define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
 #else
 # define preemptible()	0
-# define IRQ_EXIT_OFFSET HARDIRQ_OFFSET
 #endif
 
 #if defined(CONFIG_SMP) || defined(CONFIG_GENERIC_HARDIRQS)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 24a921b..f42ff97 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -343,7 +343,7 @@ void irq_exit(void)
 
 	account_irq_exit_time(current);
 	trace_hardirq_exit();
-	sub_preempt_count(IRQ_EXIT_OFFSET);
+	sub_preempt_count(HARDIRQ_OFFSET);
 	if (!in_interrupt() && local_softirq_pending())
 		invoke_softirq();
 
@@ -353,7 +353,6 @@ void irq_exit(void)
 		tick_nohz_irq_exit();
 #endif
 	rcu_irq_exit();
-	sched_preempt_enable_no_resched();
 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 	local_irq_restore(flags);
 #endif
-- 
1.7.5.4

[GIT PULL] irq: cleanups

[Frederic Weisbecker]

Hi,

Until everyone agrees on https://patchwork.kernel.org/patch/2174211/ ,
here are two commits that seem quite uncontroversial to me.

Please pull from:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	irq/urgent-for-tip

Thanks.

Frederic Weisbecker (2):
  irq: Remove IRQ_EXIT_OFFSET workaround
  irq: Don't re-enable interrupts at the end of irq_exit

 include/linux/hardirq.h |    2 --
 kernel/softirq.c        |   10 ++--------
 2 files changed, 2 insertions(+), 10 deletions(-)

-- 
1.7.5.4

[PATCH 1/2] irq: Remove IRQ_EXIT_OFFSET workaround

[Frederic Weisbecker]

The IRQ_EXIT_OFFSET trick was used to make sure the irq
doesn't get preempted after we substract the HARDIRQ_OFFSET
until we are entirely done with any code in irq_exit().

This workaround was necessary because some archs may call
irq_exit() with irqs enabled and there is still some code
in the end of this function that is not covered by the
HARDIRQ_OFFSET but want to stay non-preemptible.

Now that irq are always disabled in irq_exit(), the whole code
is guaranteed not to be preempted. We can thus remove this hack.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/hardirq.h |    2 --
 kernel/softirq.c        |    3 +--
 2 files changed, 1 insertions(+), 4 deletions(-)

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 29eb805..c1d6555 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -118,10 +118,8 @@
 
 #ifdef CONFIG_PREEMPT_COUNT
 # define preemptible()	(preempt_count() == 0 && !irqs_disabled())
-# define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
 #else
 # define preemptible()	0
-# define IRQ_EXIT_OFFSET HARDIRQ_OFFSET
 #endif
 
 #if defined(CONFIG_SMP) || defined(CONFIG_GENERIC_HARDIRQS)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 24a921b..f42ff97 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -343,7 +343,7 @@ void irq_exit(void)
 
 	account_irq_exit_time(current);
 	trace_hardirq_exit();
-	sub_preempt_count(IRQ_EXIT_OFFSET);
+	sub_preempt_count(HARDIRQ_OFFSET);
 	if (!in_interrupt() && local_softirq_pending())
 		invoke_softirq();
 
@@ -353,7 +353,6 @@ void irq_exit(void)
 		tick_nohz_irq_exit();
 #endif
 	rcu_irq_exit();
-	sched_preempt_enable_no_resched();
 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 	local_irq_restore(flags);
 #endif
-- 
1.7.5.4

[PATCH 2/2] irq: Don't re-enable interrupts at the end of irq_exit

[Frederic Weisbecker]

Commit 74eed0163d0def3fce27228d9ccf3d36e207b286
"irq: Ensure irq_exit() code runs with interrupts disabled"
restore interrupts flags in the end of irq_exit() for archs
that don't define __ARCH_IRQ_EXIT_IRQS_DISABLED.

However always returning from irq_exit() with interrupts
disabled should not be a problem for these archs. Prior to
this commit this was already happening anytime we processed
pending softirqs anyway.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/softirq.c |    7 +------
 1 files changed, 1 insertions(+), 6 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index f42ff97..dce38fa 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -334,9 +334,7 @@ static inline void invoke_softirq(void)
 void irq_exit(void)
 {
 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
-	unsigned long flags;
-
-	local_irq_save(flags);
+	local_irq_disable();
 #else
 	WARN_ON_ONCE(!irqs_disabled());
 #endif
@@ -353,9 +351,6 @@ void irq_exit(void)
 		tick_nohz_irq_exit();
 #endif
 	rcu_irq_exit();
-#ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
-	local_irq_restore(flags);
-#endif
 }
 
 /*
-- 
1.7.5.4