linux-kernel - [PATCH v5 2/5] clkdev: Fix race condition in clock lookup from device tree

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Date:	Sat, 24 Aug 2013 20:27:02 +0200
From:	Sylwester Nawrocki <sylvester.nawrocki@...il.com>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	linux@....linux.org.uk, mturquette@...aro.org,
	jiada_wang@...tor.com, linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org, linux-mips@...ux-mips.org,
	linux-sh@...r.kernel.org, s.nawrocki@...sung.com,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: [PATCH v5 2/5] clkdev: Fix race condition in clock lookup from device tree

There is currently a race condition in the device tree part of clk_get()
function, since the pointer returned from of_clk_get_by_name() may become
invalid before __clk_get() call. E.g. due to the clock provider driver
remove() callback being called in between of_clk_get_by_name() and
__clk_get().

Fix this by doing both the look up and __clk_get() operations with the
clock providers list mutex held. This ensures that the clock pointer
returned from __of_clk_get_from_provider() call and passed to __clk_get()
is valid, as long as the clock supplier module first removes its clock
provider instance and then does clk_unregister() on the corresponding
clocks.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@...sung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
Reviewed-by: Mike Turquette <mturquette@...aro.org>
Acked-by: Russell King <rmk+kernel@....linux.org.uk>
---
Changes since v2:
 - none.

Changes since v1:
 - include "clk.h".
---
 drivers/clk/clkdev.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c
index 442a313..48f6721 100644
--- a/drivers/clk/clkdev.c
+++ b/drivers/clk/clkdev.c
@@ -21,6 +21,8 @@
 #include <linux/clkdev.h>
 #include <linux/of.h>
 
+#include "clk.h"
+
 static LIST_HEAD(clocks);
 static DEFINE_MUTEX(clocks_mutex);
 
@@ -39,7 +41,13 @@ struct clk *of_clk_get(struct device_node *np, int index)
 	if (rc)
 		return ERR_PTR(rc);
 
-	clk = of_clk_get_from_provider(&clkspec);
+	of_clk_lock();
+	clk = __of_clk_get_from_provider(&clkspec);
+
+	if (!IS_ERR(clk) && !__clk_get(clk))
+		clk = ERR_PTR(-ENOENT);
+
+	of_clk_unlock();
 	of_node_put(clkspec.np);
 	return clk;
 }
@@ -157,7 +165,7 @@ struct clk *clk_get(struct device *dev, const char *con_id)
 
 	if (dev) {
 		clk = of_clk_get_by_name(dev->of_node, con_id);
-		if (!IS_ERR(clk) && __clk_get(clk))
+		if (!IS_ERR(clk))
 			return clk;
 	}
 
-- 
1.7.4.1

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