[PATCH] x86, UV: null pointer in uv_flush_tlb_others()

[cpw <cpw@sgi.com>]

The SGI UV tlb shootdown code panics the system with a null pointer
deference if 'nobau' is specified on the boot commandline.

uv_flush_tlb_other() gets called for every flush, whether the BAU is disabled
or not.  It should not be keeping the s_enters statistic while the BAU
is disabled.
The panic occurs because, during initialization, init_per_cpu_tunables()
does not set the bcp->statp pointer if nobau was specified.

The code is the same in the 3.12.2 tree.

Cc: <stable@vger.kernel.org> # 3.12.x
Signed-off-by: Cliff Wickman <cpw@sgi.com>
---
 arch/x86/platform/uv/tlb_uv.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Index: linux/arch/x86/platform/uv/tlb_uv.c
===================================================================
--- linux.orig/arch/x86/platform/uv/tlb_uv.c
+++ linux/arch/x86/platform/uv/tlb_uv.c
@@ -1070,12 +1070,13 @@ const struct cpumask *uv_flush_tlb_other
 	unsigned long status;
 
 	bcp = &per_cpu(bau_control, cpu);
-	stat = bcp->statp;
-	stat->s_enters++;
 
 	if (bcp->nobau)
 		return cpumask;
 
+	stat = bcp->statp;
+	stat->s_enters++;
+
 	if (bcp->busy) {
 		descriptor_status =
 			read_lmmr(UVH_LB_BAU_SB_ACTIVATION_STATUS_0);