Re: [PATCH] clk: Guard clk_round_rate() against error pointers

[Brian Masney <bmasney@redhat.com>]

Hi Praveen,

On Thu, Jul 23, 2026 at 10:10:06PM +0530, Praveen Talari wrote:
> On 23-07-2026 19:59, Brian Masney wrote:
> > On Thu, Jul 23, 2026 at 11:40:47AM +0530, Praveen Talari wrote:
> > > clk_round_rate() only checks for a NULL clk pointer before
> > > dereferencing it, but callers such as dev_pm_opp_set_rate() can pass
> > > it an error pointer (e.g. ERR_PTR(-ENOENT) left behind by
> > > clk_get() when a device has no Linux clock and is instead managed by
> > > firmware via a genpd/OPP performance domain).
> > > 
> > > Dereferencing that error pointer to read clk->exclusive_count
> > > crashes with an unhandled kernel NULL pointer dereference, since
> > > ERR_PTR(-ENOENT) plus the field's offset lands on a small, unmapped
> > > address:
> > > 
> > >    Unable to handle kernel NULL pointer dereference at virtual
> > >    address 000000000000002e
> > >    ...
> > >    pc : clk_round_rate+0x3c/0x188
> > >    ...
> > >    Call trace:
> > >     clk_round_rate+0x3c/0x188 (P)
> > >     dev_pm_opp_set_rate+0x114/0x33c
> > > 
> > > Change the guard from "if (!clk)" to "if (IS_ERR_OR_NULL(clk))",
> > > matching the pattern already used by other clk consumer API
> > > functions such as clk_unprepare(), so an error pointer is rejected
> > > the same way a NULL pointer is.
> > > 
> > > Signed-off-by: Praveen Talari <praveen.talari@oss.qualcomm.com>
> > > ---
> > >   drivers/clk/clk.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > > index 048adfa86a5d..8c1ad3d10284 100644
> > > --- a/drivers/clk/clk.c
> > > +++ b/drivers/clk/clk.c
> > > @@ -1780,7 +1780,7 @@ long clk_round_rate(struct clk *clk, unsigned long rate)
> > >   	struct clk_rate_request req;
> > >   	int ret;
> > > -	if (!clk)
> > > +	if (IS_ERR_OR_NULL(clk))
> > Can you provide more details about the clk_get() call point that starts this
> > error? Specifically which driver this occurs in and the exact scenario that
> > triggers this.
> 
> On SA8255P platform there is no Linux
> clock for the SE, and the perf domain device's OPPs are populated entirely
> from firmware via devm_pm_opp_of_add_table() (through
> of_genpd_add_provider_simple()/onecell()), so the perf domain's OPP table
> has entries even though no clk_get() ever succeeds for it.
> 
> The clk_get(-ENOENT) case comes from _update_opp_table_clk() in
> drivers/opp/core.c:
> 
>     opp_table->clk = clk_get(dev, NULL);
>     ret = PTR_ERR_OR_ZERO(opp_table->clk);
>     ...
>     if (ret == -ENOENT) {
>         /* ... no clk provided ... */
>         opp_table->clk_count = 1;
>         return opp_table;   /* opp_table->clk left as ERR_PTR(-ENOENT) */
>     }
> 
> Because the perf domain device has no "clocks" property (its OPPs are
> supplied purely as performance states by firmware/genpd), clk_get()
> returns -ENOENT, and opp_table->clk is left holding that error pointer
> rather than being reset to NULL.

This looks to be a reasonable change. Thanks.

Reviewed-by: Brian Masney <bmasney@redhat.com>