Subject: [PATCH RFC 2/2] clkdev: Fix race condition in clock lookup from device tree

From: [email-masked] (Mike Turquette)
Date: Mon, 19 Aug 2013 12:42:16 -0700

Quoting Sylwester Nawrocki (2013-08-09 09:34:06)
> 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. For example, 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 <[email-masked]>
> Signed-off-by: Kyungmin Park <[email-masked]>

Reviewed-by: Mike Turquette <[email-masked]>

I can take this through the clk tree if Russell's ACKs.

Regards,
Mike

> ---
>  drivers/clk/clkdev.c |   10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c
> index 442a313..4f5c4ef 100644
> --- a/drivers/clk/clkdev.c
> +++ b/drivers/clk/clkdev.c
> @@ -39,7 +39,13 @@ 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 +163,7 @@ 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