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[PATCH v2 4/4] clkdev: Fix race condition in clock lookup from device tr

To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 4/4] clkdev: Fix race condition in clock lookup from device tree
From: Sylwester Nawrocki <s.nawrocki@samsung.com>
Date: Tue, 20 Aug 2013 19:34:23 +0200
Cc: linux@arm.linux.org.uk, mturquette@linaro.org, jiada_wang@mentor.com, robherring2@gmail.com, grant.likely@linaro.org, broonie@kernel.org, vapier@gentoo.org, ralf@linux-mips.org, kyungmin.park@samsung.com, shawn.guo@linaro.org, sebastian.hesselbarth@gmail.com, LW@KARO-electronics.de, t.figa@samsung.com, g.liakhovetski@gmx.de, laurent.pinchart@ideasonboard.com, linux-kernel@vger.kernel.org, uclinux-dist-devel@blackfin.uclinux.org, linux-mips@linux-mips.org, linux-sh@vger.kernel.org, Sylwester Nawrocki <s.nawrocki@samsung.com>
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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 <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Mike Turquette <mturquette@linaro.org>
---
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();
        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;
        }

--
1.7.9.5


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