[PATCH 3.12 120/122] x86: UV BAU: Avoid NULL pointer reference in ptc_seq_show

[Jiri Slaby]

From: James Custer <jcuster@xxxxxxx>

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

===============

commit fa2a79ce6aef5de35a4d50487da35deb6b634944 upstream.

In init_per_cpu(), when get_cpu_topology() fails, init_per_cpu_tunables()
is not called afterwards. This means that bau_control->statp is NULL.
If a user then reads /proc/sgi_uv/ptc_statistics ptc_seq_show() references
a NULL pointer. Therefore, since uv_bau_init calls set_bau_off when
init_per_cpu() fails, we add code that detects when the bau is off in
ptc_seq_show() to avoid referencing a NULL pointer.

Signed-off-by: James Custer <jcuster@xxxxxxx>
Cc: Russ Anderson <rja@xxxxxxx>
Link: http://lkml.kernel.org/r/1414952199-185319-2-git-send-email-jcuster@xxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 arch/x86/platform/uv/tlb_uv.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
index efe4d7220397..a6b5affb024a 100644
--- a/arch/x86/platform/uv/tlb_uv.c
+++ b/arch/x86/platform/uv/tlb_uv.c
@@ -1367,6 +1367,10 @@ static int ptc_seq_show(struct seq_file *file, void *data)
 	}
 	if (cpu < num_possible_cpus() && cpu_online(cpu)) {
 		bcp = &per_cpu(bau_control, cpu);
+		if (bcp->nobau) {
+			seq_printf(file, "cpu %d bau disabled\n", cpu);
+			return 0;
+		}
 		stat = bcp->statp;
 		/* source side statistics */
 		seq_printf(file,
-- 
2.2.2

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