[tip:x86/urgent] x86/UV: Fix NULL pointer dereference in uv_flush_tlb_others() if the 'nobau' boot option is used

[tip-bot for cpw <tipbot@zytor.com>]

Commit-ID:  3eae49ca8954f958b2001ab5643ef302cb7b67c7
Gitweb:     http://git.kernel.org/tip/3eae49ca8954f958b2001ab5643ef302cb7b67c7
Author:     cpw <cpw@sgi.com>
AuthorDate: Tue, 3 Dec 2013 17:15:30 -0600
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 10 Dec 2013 10:06:00 +0100

x86/UV: Fix NULL pointer dereference in uv_flush_tlb_others() if the 'nobau' boot option is used

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@sgi.com>
Cc: <stable@vger.kernel.org> # 3.12.x
Link: http://lkml.kernel.org/r/E1VnzBi-0005yF-MU@eag09.americas.sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/platform/uv/tlb_uv.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
index 0f92173..efe4d72 100644
--- 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_others(const struct cpumask *cpumask,
 	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);