[PATCH 1/1] powerpc: Clear cpu_sibling_map in cpu_die

[Brian King]

While testing CPU DLPAR, the following problem was discovered.
We were DLPAR removing the first CPU, which in this case was
logical CPUs 0-3. CPUs 0-2 were already marked offline and
we were in the process of offlining CPU 3. After marking
the CPU inactive and offline in cpu_disable, but before the
cpu was completely idle (cpu_die), we ended up in __make_request
on CPU 3. There we looked at the topology map to see which CPU
to complete the I/O on and found no CPUs in the cpu_sibling_map.
This resulted in the block layer setting the completion cpu
to be NR_CPUS, which then caused an oops when we tried to
complete the I/O.

Fix this by delaying clearing the sibling map of the cpu we
are offlining for the cpu we are offlining until cpu_die.

Signed-off-by: Brian King <brking at linux.vnet.ibm.com>
---

 arch/powerpc/kernel/smp.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff -puN arch/powerpc/kernel/smp.c~powerpc_sibling_map_offline arch/powerpc/kernel/smp.c
--- linux-2.6/arch/powerpc/kernel/smp.c~powerpc_sibling_map_offline	2010-08-09 16:49:47.000000000 -0500
+++ linux-2.6-bjking1/arch/powerpc/kernel/smp.c	2010-08-09 16:49:47.000000000 -0500
@@ -598,8 +598,11 @@ int __cpu_disable(void)
 	/* Update sibling maps */
 	base = cpu_first_thread_in_core(cpu);
 	for (i = 0; i < threads_per_core; i++) {
-		cpumask_clear_cpu(cpu, cpu_sibling_mask(base + i));
-		cpumask_clear_cpu(base + i, cpu_sibling_mask(cpu));
+		if ((base + i) != cpu) {
+			cpumask_clear_cpu(cpu, cpu_sibling_mask(base + i));
+			cpumask_clear_cpu(base + i, cpu_sibling_mask(cpu));
+		}
+
 		cpumask_clear_cpu(cpu, cpu_core_mask(base + i));
 		cpumask_clear_cpu(base + i, cpu_core_mask(cpu));
 	}
@@ -641,6 +644,8 @@ void cpu_hotplug_driver_unlock()
 
 void cpu_die(void)
 {
+	cpumask_clear_cpu(smp_processor_id(), cpu_sibling_mask(smp_processor_id()));
+
 	if (ppc_md.cpu_die)
 		ppc_md.cpu_die();
 }
_