[PATCH 3.12 068/118] x86/UV: Fix NULL pointer dereference in uv_flush_tlb_others() if the nobau boot option is used

[Greg Kroah-Hartman]

3.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: cpw <cpw@xxxxxxx>

commit 3eae49ca8954f958b2001ab5643ef302cb7b67c7 upstream.

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.

Signed-off-by: Cliff Wickman <cpw@xxxxxxx>
Link: http://lkml.kernel.org/r/E1VnzBi-0005yF-MU@xxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/x86/platform/uv/tlb_uv.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/arch/x86/platform/uv/tlb_uv.c
+++ b/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);


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