linux-kernel - [PATCH 2/2] x86: UV BAU Avoid NULL pointer reference in ptc_seq

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Date:	Sun,  2 Nov 2014 12:16:39 -0600
From:	James Custer <jcuster@....com>
To:	x86@...nel.org
Cc:	James Custer <jcuster@....com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>, Russ Anderson <rja@....com>
Subject: [PATCH 2/2] x86: UV BAU Avoid NULL pointer reference in ptc_seq_show

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@....com>
---
 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 3968d67..570b1b1 100644
--- a/arch/x86/platform/uv/tlb_uv.c
+++ b/arch/x86/platform/uv/tlb_uv.c
@@ -1384,6 +1384,10 @@ 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,
-- 
1.7.12.4

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