linux-kernel - [PATCH] PowerPC: Fix num_cpus calculation in smp_call_function

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Message-Id: <200707311519.48359.kevcorry@us.ibm.com>
Date:	Tue, 31 Jul 2007 15:19:46 -0500
From:	Kevin Corry <kevcorry@...ibm.com>
To:	linuxppc-dev@...abs.org, LKML <linux-kernel@...r.kernel.org>
Cc:	Carl Love <carll@...ibm.com>
Subject: [PATCH] PowerPC: Fix num_cpus calculation in smp_call_function_map()

[POWERPC]: Fix num_cpus calculation in smp_call_function_map().

In smp_call_function_map(), num_cpus is set to the number of online CPUs minus
one. However, if the CPU mask does not include all CPUs (except the one we're
running on), the routine will hang in the first while() loop until the 8 second
timeout occurs.

The num_cpus should be set to the number of CPUs specified in the mask passed
into the routine, after we've made any modifications to the mask. With this
change, we can also get rid of the call to cpus_empty() and avoid adding
another pass through the bitmask.

Signed-off-by: Kevin Corry <kevcorry@...ibm.com>
Signed-off-by: Carl Love <carll@...ibm.com>

Index: linux-2.6.23-rc1/arch/powerpc/kernel/smp.c
===================================================================
--- linux-2.6.23-rc1.orig/arch/powerpc/kernel/smp.c
+++ linux-2.6.23-rc1/arch/powerpc/kernel/smp.c
@@ -212,11 +212,6 @@ int smp_call_function_map(void (*func) (
 		atomic_set(&data.finished, 0);
 
 	spin_lock(&call_lock);
-	/* Must grab online cpu count with preempt disabled, otherwise
-	 * it can change. */
-	num_cpus = num_online_cpus() - 1;
-	if (!num_cpus)
-		goto done;
 
 	/* remove 'self' from the map */
 	if (cpu_isset(smp_processor_id(), map))
@@ -224,7 +219,9 @@ int smp_call_function_map(void (*func) (
 
 	/* sanity check the map, remove any non-online processors. */
 	cpus_and(map, map, cpu_online_map);
-	if (cpus_empty(map))
+
+	num_cpus = cpus_weight(map);
+	if (!num_cpus)
 		goto done;
 
 	call_data = &data;
-
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