linux-kernel - Re: [RESEND PATCH v2 10/16] clk: move checking .git_parent to __clk_core

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Date:	Mon, 1 Feb 2016 18:39:22 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:	linux-clk@...r.kernel.org,
	Michael Turquette <mturquette@...libre.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH v2 10/16] clk: move checking .git_parent to
 __clk_core_init()

On 02/02, Masahiro Yamada wrote:
> 2016-02-02 9:50 GMT+09:00 Stephen Boyd <sboyd@...eaurora.org>:
> > On 12/28, Masahiro Yamada wrote:
> >> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> >> index e6e10f5..4ad0a36 100644
> >> --- a/drivers/clk/clk.c
> >> +++ b/drivers/clk/clk.c
> >> @@ -1677,13 +1677,6 @@ static struct clk_core *__clk_init_parent(struct clk_core *core)
> >>               goto out;
> >>       }
> >>
> >> -     if (!core->ops->get_parent) {
> >> -             WARN(!core->ops->get_parent,
> >> -                     "%s: multi-parent clocks must implement .get_parent\n",
> >> -                     __func__);
> >> -             goto out;
> >> -     }
> >> -
> >>       /*
> >>        * Do our best to cache parent clocks in core->parents.  This prevents
> >>        * unnecessary and expensive lookups.  We don't set core->parent here;
> >> @@ -2315,6 +2308,11 @@ static int __clk_core_init(struct clk_core *core)
> >>               goto out;
> >>       }
> >>
> >> +     if (core->num_parents > 1 && !core->ops->get_parent) {
> >> +             pr_err("%s: %s must implement .get_parent as it has multi parents\n",
> >> +                    __func__, core->name);
> >> +     }
> >> +
> >
> > This would seem to allow a case where we may deref a null
> > get_parent op if it isn't set and we call __clk_init_parent().
> > The next patch removes that case by restructuring
> > __clk_init_parent(), so we should just combine these two patches
> > together and that theoretical problem goes away.
> >
> 
> I think the case never happens.
> 
> __clk_init_parent() is a static function that is only called from
> __clk_core_init().
> So, the null pointer for .get_parent() has been already checked before
> __clk_init_parent().
> 

Right, this patch moves the check to __clk_core_init(), and it
will print an error and then keep going (because we lost the goto
out part). Once we keep going in __clk_core_init() we'll call
__clk_init_parent() and NULL pointer deref.

-- 
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