linux-kernel - [PATCH 3.2 079/131] MIPS: OCTEON: make get_system

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Message-ID: <lsq.1410438733.132759756@decadent.org.uk>
Date:	Thu, 11 Sep 2014 13:32:13 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "James Hogan" <james.hogan@...tec.com>,
	"Aaro Koskinen" <aaro.koskinen@....com>,
	"Markos Chandras" <markos.chandras@...tec.com>
Subject: [PATCH 3.2 079/131] MIPS: OCTEON: make get_system_type() thread-safe

3.2.63-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Aaro Koskinen <aaro.koskinen@....com>

commit 608308682addfdc7b8e2aee88f0e028331d88e4d upstream.

get_system_type() is not thread-safe on OCTEON. It uses static data,
also more dangerous issue is that it's calling cvmx_fuse_read_byte()
every time without any synchronization. Currently it's possible to get
processes stuck looping forever in kernel simply by launching multiple
readers of /proc/cpuinfo:

	(while true; do cat /proc/cpuinfo > /dev/null; done) &
	(while true; do cat /proc/cpuinfo > /dev/null; done) &
	...

Fix by initializing the system type string only once during the early
boot.

Signed-off-by: Aaro Koskinen <aaro.koskinen@....com>
Reviewed-by: Markos Chandras <markos.chandras@...tec.com>
Patchwork: http://patchwork.linux-mips.org/patch/7437/
Signed-off-by: James Hogan <james.hogan@...tec.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/mips/cavium-octeon/setup.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

--- a/arch/mips/cavium-octeon/setup.c
+++ b/arch/mips/cavium-octeon/setup.c
@@ -266,6 +266,18 @@ static irqreturn_t octeon_rlm_interrupt(
 }
 #endif
 
+static char __read_mostly octeon_system_type[80];
+
+static int __init init_octeon_system_type(void)
+{
+	snprintf(octeon_system_type, sizeof(octeon_system_type), "%s (%s)",
+		cvmx_board_type_to_string(octeon_bootinfo->board_type),
+		octeon_model_get_string(read_c0_prid()));
+
+	return 0;
+}
+early_initcall(init_octeon_system_type);
+
 /**
  * Return a string representing the system type
  *
@@ -273,11 +285,7 @@ static irqreturn_t octeon_rlm_interrupt(
  */
 const char *octeon_board_type_string(void)
 {
-	static char name[80];
-	sprintf(name, "%s (%s)",
-		cvmx_board_type_to_string(octeon_bootinfo->board_type),
-		octeon_model_get_string(read_c0_prid()));
-	return name;
+	return octeon_system_type;
 }
 
 const char *get_system_type(void)

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