Commit 4d4c4e24 authored Feb 22, 2013 by Frederic Weisbecker

irq: Remove IRQ_EXIT_OFFSET workaround



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>

parent af7bdbaf

include/linux/hardirq.h

+0 −2

Original line number	Diff line number	Diff line
		@@ -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)

kernel/softirq.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -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