linux-kernel - [PATCH 1/2] UV: NMI: insert per_cpu accessor function on uv_hub

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Date:	Sat, 12 Sep 2015 21:51:05 -0500 (CDT)
From:	George Beshers <gbeshers@....com>
To:	George Beshers <gbeshers@....com>, Mike Travis <travis@....com>,
	linux-kernel@...r.kernel.org, Alex Thorlton <athorlton@....com>,
	Dimitri Sivanich <sivanich@....com>,
	Ingo Molnar <mingo@...hat.com>, Hedi Berriche <hedi@....com>,
	Russ Anderson <rja@....com>
Cc:	George Beshers <gbeshers@....com>
Subject: [PATCH 1/2] UV: NMI: insert per_cpu accessor function on uv_hub_nmi.

UV: NMI: insert this_cpu_read accessor function on uv_hub_nmi.

On SGI UV systems a 'power nmi' command from the CMC causes
all processors to drop into uv_handle_nmi().  With the 4.0
kernel this results in

    BUG: unable to handle kernel paging request

The bug is caused by the current code trying to use the PER_CPU
variable uv_cpu_nmi.hub without an appropriate accessor function.
That oversight occurred in

    commit e16321709c82 ("uv: Replace __get_cpu_var")
    Author: Christoph Lameter <cl@...ux.com>
    Date:   Sun Aug 17 12:30:41 2014 -0500

This patch inserts this_cpu_read() in the uv_hub_nmi macro restoring
the intended functionality.

Signed-off-by: George Beshers <gbeshers@....com>
Acked-by: Mike Travis <travis@....com>
Cc: Russ Anderson <rja@....com>
Cc: Dimitri Sivanich <sivanich@....com>
Cc: Hedi Berriche <hedi@....com>
Cc: Alex Thorlton <athorlton@....com>
Cc: Christoph Lameter <cl@...ux.com>

diff --git a/arch/x86/include/asm/uv/uv_hub.h b/arch/x86/include/asm/uv/uv_hub.h
index a00ad8f..ea707478 100644
--- a/arch/x86/include/asm/uv/uv_hub.h
+++ b/arch/x86/include/asm/uv/uv_hub.h
@@ -609,7 +609,7 @@ struct uv_cpu_nmi_s {
 
 DECLARE_PER_CPU(struct uv_cpu_nmi_s, uv_cpu_nmi);
 
-#define uv_hub_nmi			(uv_cpu_nmi.hub)
+#define uv_hub_nmi			this_cpu_read(uv_cpu_nmi.hub)
 #define uv_cpu_nmi_per(cpu)		(per_cpu(uv_cpu_nmi, cpu))
 #define uv_hub_nmi_per(cpu)		(uv_cpu_nmi_per(cpu).hub)
 
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