[PATCH] x86-64: Use physflat on Intel for < 8 CPUs with CPU hotplug

This avoids races with the APIC broadcast/mask modes.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/arch/x86_64/kernel/genapic.c b/arch/x86_64/kernel/genapic.c
index fe416fd4dbe0..7a64ea181788 100644
--- a/arch/x86_64/kernel/genapic.c
+++ b/arch/x86_64/kernel/genapic.c
@@ -104,9 +104,14 @@ void __init clustered_apic_check(void)
          * (We don't use lowest priority delivery + HW APIC IRQ steering, so
          * can ignore the clustered logical case and go straight to physical.)
          */
-        if (clusters <= 1 && max_cluster <= 8 && cluster_cnt[0] == max_cluster)
+        if (clusters <= 1 && max_cluster <= 8 && cluster_cnt[0] == max_cluster) {
+#ifdef CONFIG_HOTPLUG_CPU
+                /* Don't use APIC shortcuts in CPU hotplug to avoid races */
+                genapic = &apic_physflat;
+#else
                 genapic = &apic_flat;
-        else
+#endif
+        } else
                 genapic = &apic_cluster;
 
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