Re: [PATCH v2] opp: Use clk_get_optional() to avoid leaving opp_table->clk as an error pointer

[Sebastian Reichel <sre@kernel.org>]

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Hi,

On Sat, Jul 25, 2026 at 11:58:22PM +0530, Praveen Talari wrote:
> _update_opp_table_clk() uses clk_get(dev, NULL) to acquire the
> device's clock. On platforms where the perf domain device has no
> Linux clock and is instead managed entirely by firmware via
> devm_pm_opp_of_add_table() (through
> of_genpd_add_provider_simple()/onecell()), clk_get() returns
> -ENOENT. That case is treated as valid (the OPP table can still
> have entries sourced from firmware), but opp_table->clk is left
> holding ERR_PTR(-ENOENT) rather than being reset to NULL:
> 
> 	opp_table->clk = clk_get(dev, NULL);
> 	ret = PTR_ERR_OR_ZERO(opp_table->clk);
> 	...
> 	if (ret == -ENOENT) {
> 		opp_table->clk_count = 1;
> 		return opp_table;   /* opp_table->clk is still ERR_PTR(-ENOENT) */
> 	}
> 
> Consumers that only check IS_ERR(opp_table->clk) treat this as a
> valid clk and pass it straight into the clk consumer API. In
> particular, dev_pm_opp_set_rate() calls
> clk_round_rate(opp_table->clk, target_freq), and clk_round_rate()
> only guards against a NULL clk, so it dereferences the error pointer
> to read clk->exclusive_count and crashes:
> 
>   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
> 
> Rather than teaching every clk consumer API to special-case
> ERR_PTR(-ENOENT), fix it at the source: use clk_get_optional()
> instead of clk_get() in _update_opp_table_clk(), which already
> translates -ENOENT into a NULL clk. This documents that the clock is
> genuinely optional for such devices, and keeps opp_table->clk holding
> either a valid clk or NULL, never a lingering -ENOENT error pointer.
> _opp_config_clk_single() is only wired up via opp_table->config_clks
> when a clk was actually found, and every other opp_table->clk
> consumer already tolerates NULL through the standard clk API (which
> treats a NULL clk as a no-op), so no other call site needs to change.
> 
> Suggested-by: Sebastian Reichel <sre@kernel.org>
> Signed-off-by: Praveen Talari <praveen.talari@oss.qualcomm.com>

Reviewed-by: Sebastian Reichel <sre@kernel.org>

Greetings,

-- Sebastian

> ---
> Changes in v2:
> - Switched from guarding clk_round_rate() against error pointers to
>   fixing the root cause in OPP core: use clk_get_optional() instead
>   of clk_get() in _update_opp_table_clk(), so opp_table->clk is left
>   as NULL (not ERR_PTR(-ENOENT)) when a device has no Linux clock,
>   per Sebastian Reichel's review suggestion.
> - Dropped the drivers/clk/clk.c change entirely.
> - Link to v1: https://patch.msgid.link/20260723-fix_ptr_check_on_clk-v1-1-568a7ed87746@oss.qualcomm.com
> ---
>  drivers/opp/core.c | 51 ++++++++++++++++++++++++---------------------------
>  1 file changed, 24 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index b6966e509f7d..80da241d40f5 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -1591,39 +1591,36 @@ static struct opp_table *_update_opp_table_clk(struct device *dev,
>  	    opp_table->clks)
>  		return opp_table;
>  
> -	/* Find clk for the device */
> -	opp_table->clk = clk_get(dev, NULL);
> +	/*
> +	 * There are few platforms which don't want the OPP core to manage
> +	 * device's clock settings. In such cases neither the platform
> +	 * provides the clks explicitly to us, nor the DT contains a valid
> +	 * clk entry. The OPP nodes in DT may still contain "opp-hz" property
> +	 * though, which we need to parse and allow the platform to find an
> +	 * OPP based on freq later on.
> +	 *
> +	 * This is a simple solution to take care of such corner cases, i.e.
> +	 * make the clk_count 1, which lets us allocate space for frequency
> +	 * in opp->rates and also parse the entries in DT. Use
> +	 * clk_get_optional() instead of clk_get() so opp_table->clk stays
> +	 * NULL for such devices, instead of holding an ERR_PTR(-ENOENT) that
> +	 * consumers must remember to special-case.
> +	 */
> +	opp_table->clk = clk_get_optional(dev, NULL);
>  
>  	ret = PTR_ERR_OR_ZERO(opp_table->clk);
> -	if (!ret) {
> -		opp_table->config_clks = _opp_config_clk_single;
> -		opp_table->clk_count = 1;
> -		return opp_table;
> +	if (ret) {
> +		dev_pm_opp_put_opp_table(opp_table);
> +		dev_err_probe(dev, ret, "Couldn't find clock\n");
> +		return ERR_PTR(ret);
>  	}
>  
> -	if (ret == -ENOENT) {
> -		/*
> -		 * There are few platforms which don't want the OPP core to
> -		 * manage device's clock settings. In such cases neither the
> -		 * platform provides the clks explicitly to us, nor the DT
> -		 * contains a valid clk entry. The OPP nodes in DT may still
> -		 * contain "opp-hz" property though, which we need to parse and
> -		 * allow the platform to find an OPP based on freq later on.
> -		 *
> -		 * This is a simple solution to take care of such corner cases,
> -		 * i.e. make the clk_count 1, which lets us allocate space for
> -		 * frequency in opp->rates and also parse the entries in DT.
> -		 */
> -		opp_table->clk_count = 1;
> -
> -		dev_dbg(dev, "%s: Couldn't find clock: %d\n", __func__, ret);
> -		return opp_table;
> -	}
> +	if (opp_table->clk)
> +		opp_table->config_clks = _opp_config_clk_single;
>  
> -	dev_pm_opp_put_opp_table(opp_table);
> -	dev_err_probe(dev, ret, "Couldn't find clock\n");
> +	opp_table->clk_count = 1;
>  
> -	return ERR_PTR(ret);
> +	return opp_table;
>  }
>  
>  /*
> 
> ---
> base-commit: b4515cf4156356e8f4fe6e0fdc17f59adab9772f
> change-id: 20260723-fix_ptr_check_on_clk-603605c3e350
> 
> Best regards,
> --  
> Praveen Talari <praveen.talari@oss.qualcomm.com>
> 

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