linux-kernel - Re: [PATCH v3 3/8] clk: Don't try to use a struct clk* after it could have been freed

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Date:	Thu, 9 Oct 2014 13:27:33 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:	Mike Turquette <mturquette@...aro.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/8] clk: Don't try to use a struct clk* after it
 could have been freed

On 10/09, Tomeu Vizoso wrote:
> As __clk_release could call kfree on clk and then we wouldn't have a safe way
> of getting the module that owns the clock.
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>

It would be good to mark this as a "Fixes:".

> ---
>  drivers/clk/clk.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index d0712b7..40aa7ad 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -2268,14 +2268,16 @@ int __clk_get(struct clk *clk)
>  
>  void __clk_put(struct clk *clk)
>  {
> +	struct module *owner;
> +
>  	if (!clk || WARN_ON_ONCE(IS_ERR(clk)))
>  		return;
>  
>  	clk_prepare_lock();
> +	owner = clk->owner;
>  	kref_put(&clk->ref, __clk_release);
> +	module_put(owner);
>  	clk_prepare_unlock();
> -
> -	module_put(clk->owner);

We don't need to move this call under the prepare lock though, right?

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