[v2,4/4] clkdev: Fix race condition in clock lookup from device tree

Commit Message

Sylwester Nawrocki/Kernel \(PLT\) /SRPOL/Staff Engineer/Samsung Electronics Aug. 20, 2013, 5:34 p.m. UTC

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. I.e. 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 <[e-mail]>
Signed-off-by: Kyungmin Park <[e-mail]>
Reviewed-by: Mike Turquette <[e-mail]>
---
Changes since v1:
 - include "clk.h".
---
 drivers/clk/clkdev.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--
1.7.9.5

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Comments

Russell King - ARM Linux Aug. 20, 2013, 9:52 p.m. UTC | #1

On Tue, Aug 20, 2013 at 07:34:23PM +0200, Sylwester Nawrocki wrote:
> 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. I.e. 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 <[e-mail]>
> Signed-off-by: Kyungmin Park <[e-mail]>
> Reviewed-by: Mike Turquette <[e-mail]>

Thanks.

Acked-by: Russell King <[e-mail]>
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Patch

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;
 	}