linux-kernel - [PATCH] Remove WARN_ON_ONCE in __smp_call_function_single and smp_call_function

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Date:	Sat, 5 Jan 2013 12:26:42 +0800
From:	Hui Zhu <teawater@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Nazarewicz <mina86@...a86.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Cc:	Zhu Yanhai <gaoyang.zyh@...bao.com>
Subject: [PATCH] Remove WARN_ON_ONCE in __smp_call_function_single and smp_call_function_single

The comments of these WARN_ON_ONCE said "Can deadlock when called with
interrupts disabled".
But I didn't find anything that will block this function.

So I think maybe this WARN_ON_ONCE is not need now.  So I post a patch for that.

Signed-off-by: Hui Zhu <teawater@...il.com>
Signed-off-by: Zhu Yanhai <gaoyang.zyh@...bao.com>

--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -303,25 +303,13 @@ int smp_call_function_single(int cpu, sm
 		.flags = 0,
 	};
 	unsigned long flags;
-	int this_cpu;
 	int err = 0;

 	/*
 	 * prevent preemption and reschedule on another processor,
 	 * as well as CPU removal
 	 */
-	this_cpu = get_cpu();
-
-	/*
-	 * Can deadlock when called with interrupts disabled.
-	 * We allow cpu's that are not yet online though, as no one else can
-	 * send smp call function interrupt to this cpu and as such deadlocks
-	 * can't happen.
-	 */
-	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
-		     && !oops_in_progress);
-
-	if (cpu == this_cpu) {
+	if (cpu == get_cpu()) {
 		local_irq_save(flags);
 		func(info);
 		local_irq_restore(flags);
@@ -409,17 +397,7 @@ void __smp_call_function_single(int cpu,
 	unsigned int this_cpu;
 	unsigned long flags;

-	this_cpu = get_cpu();
-	/*
-	 * Can deadlock when called with interrupts disabled.
-	 * We allow cpu's that are not yet online though, as no one else can
-	 * send smp call function interrupt to this cpu and as such deadlocks
-	 * can't happen.
-	 */
-	WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
-		     && !oops_in_progress);
-
-	if (cpu == this_cpu) {
+	if (cpu == get_cpu()) {
 		local_irq_save(flags);
 		data->func(data->info);
 		local_irq_restore(flags);
--
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