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@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Mike Turquette <mturquette@linaro.org>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c
index 442a313..48f6721 100644 (file)
--- 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;
        }