linux-kernel - [PATCH] Ignore bogus ACPI info for offline CPUs

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Date:	Sat, 19 May 2007 16:22:50 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Len Brown <lenb@...nel.org>, Darren Hart <dvhltc@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, Andrew Morton <akpm@...l.org>,
	Stable Team <stable@...nel.org>
Subject: [PATCH] Ignore bogus ACPI info for offline CPUs

Booting a SMP kernel with maxcpus=1 on a SMP system leads to a hard
hang, because ACPI ignores the maxcpus setting and sends timer broadcast
info for the offline CPUs. This results in a stuck for ever call to
smp_call_function_single() on an offline CPU.

Ignore the bogus information and print a kernel error to remind ACPI
folks to fix it.

Affects 2.6.21 / 2.6.22-rc

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Index: linux-2.6.22-rc/kernel/time/tick-broadcast.c
===================================================================
--- linux-2.6.22-rc.orig/kernel/time/tick-broadcast.c
+++ linux-2.6.22-rc/kernel/time/tick-broadcast.c
@@ -244,11 +244,18 @@ void tick_broadcast_on_off(unsigned long
 {
 	int cpu = get_cpu();
 
-	if (cpu == *oncpu)
-		tick_do_broadcast_on_off(&reason);
-	else
-		smp_call_function_single(*oncpu, tick_do_broadcast_on_off,
-					 &reason, 1, 1);
+	if (!cpu_isset(*oncpu, cpu_online_map)) {
+		printk(KERN_ERR "tick-braodcast: ignoring broadcast for "
+		       "offline CPU #%d\n", *oncpu);
+	} else {
+
+		if (cpu == *oncpu)
+			tick_do_broadcast_on_off(&reason);
+		else
+			smp_call_function_single(*oncpu,
+						 tick_do_broadcast_on_off,
+						 &reason, 1, 1);
+	}
 	put_cpu();
 }
 


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