linux-kernel - Re: [PATCH] clk: prevent erronous parsing of children during rate change

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Date:	Wed, 03 Sep 2014 12:22:03 -0700
From:	Mike Turquette <mturquette@...aro.org>
To:	Tero Kristo <t-kristo@...com>, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, tony@...mide.com, nm@...com
Cc:	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] clk: prevent erronous parsing of children during rate change

Quoting Tero Kristo (2014-08-21 06:47:45)
> In some cases, clocks can switch their parent with clk_set_rate, for
> example clk_mux can do this in some cases. Current implementation of
> clk_change_rate uses un-safe list iteration on the clock children, which
> will cause wrong clocks to be parsed in case any of the clock children
> change their parents during the change rate operation. Fixed by using
> the safe list iterator instead.
> 
> The problem was detected due to some divide by zero errors generated
> by clock init on dra7-evm board, see discussion under
> http://article.gmane.org/gmane.linux.ports.arm.kernel/349180 for details.
> 
> Signed-off-by: Tero Kristo <t-kristo@...com>
> To: Mike Turquette <mturquette@...aro.org>
> Reported-by: Nishanth Menon <nm@...com>

Applied to clk-fixes.

Thanks!
Mike

> ---
>  drivers/clk/clk.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index b76fa69..bacc06f 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1467,6 +1467,7 @@ static struct clk *clk_propagate_rate_change(struct clk *clk, unsigned long even
>  static void clk_change_rate(struct clk *clk)
>  {
>         struct clk *child;
> +       struct hlist_node *tmp;
>         unsigned long old_rate;
>         unsigned long best_parent_rate = 0;
>         bool skip_set_rate = false;
> @@ -1502,7 +1503,11 @@ static void clk_change_rate(struct clk *clk)
>         if (clk->notifier_count && old_rate != clk->rate)
>                 __clk_notify(clk, POST_RATE_CHANGE, old_rate, clk->rate);
>  
> -       hlist_for_each_entry(child, &clk->children, child_node) {
> +       /*
> +        * Use safe iteration, as change_rate can actually swap parents
> +        * for certain clock types.
> +        */
> +       hlist_for_each_entry_safe(child, tmp, &clk->children, child_node) {
>                 /* Skip children who will be reparented to another clock */
>                 if (child->new_parent && child->new_parent != clk)
>                         continue;
> -- 
> 1.7.9.5
> 
--
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