linux-kernel - [PATCH] smp.c: Quit unconditionally enabling irqs in on_each_cpu

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Date:	Thu,  8 Aug 2013 11:25:42 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	linux-kernel@...r.kernel.org
Cc:	Christoph Lameter <cl@...ux.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	David Daney <david.daney@...ium.com>
Subject: [PATCH] smp.c: Quit unconditionally enabling irqs in on_each_cpu_mask().

From: David Daney <david.daney@...ium.com>

As in f21afc25f9ed (smp.h: Use local_irq_{save,restore}() in !SMP
version of on_each_cpu().), we don't want to enable irqs if they are
not already enabled.

I don't know of any bugs currently caused by this unconditional
local_irq_enable(), but I want to use this function in MIPS/OCTEON
early boot (when we have early_boot_irqs_disabled).  This also makes
this function have similar semantics to on_each_cpu() which is good in
itself.

Signed-off-by: David Daney <david.daney@...ium.com>
---
 kernel/smp.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index 91c52ab..97edbbe 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -578,8 +578,10 @@ EXPORT_SYMBOL(on_each_cpu);
  *
  * If @wait is true, then returns once @func has returned.
  *
- * You must not call this function with disabled interrupts or
- * from a hardware interrupt handler or from a bottom half handler.
+ * You must not call this function with disabled interrupts or from a
+ * hardware interrupt handler or from a bottom half handler.  The
+ * exception is that it may be used during early boot while
+ * early_boot_irqs_disabled is set.
  */
 void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
 			void *info, bool wait)
@@ -588,9 +590,10 @@ void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
 
 	smp_call_function_many(mask, func, info, wait);
 	if (cpumask_test_cpu(cpu, mask)) {
-		local_irq_disable();
+		unsigned long flags;
+		local_irq_save(flags);
 		func(info);
-		local_irq_enable();
+		local_irq_restore(flags);
 	}
 	put_cpu();
 }
-- 
1.7.11.7

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