linux-kernel - Re: [PATCH] clk: fix possible circular locking in clk_notifier

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Date:   Thu, 10 Jun 2021 09:23:30 +0200
From:   Sean Nyekjaer <sean@...nix.com>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: fix possible circular locking in
 clk_notifier_register()

On 10/06/2021 09.17, Sean Nyekjaer wrote:
> Allocating memory with prepare_lock mutex held makes lockdep unhappy
> when memory pressure makes the system do fs_reclaim on eg. rawnand using
> clk.
> 
> Push the allocation outside the lock.
> 
[...]
> 
> Signed-off-by: Sean Nyekjaer <sean@...nix.com>
Fixes: b2476490ef111 ("clk: introduce the common clock framework")

We could possibly add this fixes tag ^^
> ---
>  drivers/clk/clk.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 65508eb89ec9..c32b71b08ccb 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -4340,17 +4340,20 @@ int clk_notifier_register(struct clk *clk, struct notifier_block *nb)
>  	if (!clk || !nb)
>  		return -EINVAL;
>  
> +	/* allocate new clk_notifier */
> +	cn = kzalloc(sizeof(*cn), GFP_KERNEL);
> +	if (!cn)
> +		goto out;
> +
>  	clk_prepare_lock();
>  
>  	/* search the list of notifiers for this clk */
>  	list_for_each_entry(cn, &clk_notifier_list, node)
> -		if (cn->clk == clk)
> +		if (cn->clk == clk) {
> +			/* if clk is in the notifier list, free new clk_notifier */
> +			kfree(cn);
>  			goto found;
> -
> -	/* if clk wasn't in the notifier list, allocate new clk_notifier */
> -	cn = kzalloc(sizeof(*cn), GFP_KERNEL);
> -	if (!cn)
> -		goto out;
> +		}
>  
>  	cn->clk = clk;
>  	srcu_init_notifier_head(&cn->notifier_head);
> @@ -4362,9 +4365,9 @@ int clk_notifier_register(struct clk *clk, struct notifier_block *nb)
>  
>  	clk->core->notifier_count++;
>  
> -out:
>  	clk_prepare_unlock();
>  
> +out:
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(clk_notifier_register);
>