[PATCH v7 3/5] clkdev: Fix race condition in clock lookup from devicetree

From: Sylwester Nawrocki
Date: Tue Oct 29 2013 - 15:53:18 EST

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

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

Signed-off-by: Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx>
Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
Reviewed-by: Mike Turquette <mturquette@xxxxxxxxxx>
Acked-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Changes since v6:
- none.

Changes since v1:
- include "clk.h".
drivers/clk/clkdev.c | 12 ++++++++++--
1 file 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();
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;


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