linux-kernel - Re: [PATCH 2/2] OPP: fix dev_pm_opp_find_bw_*() when bandwidth table not initialized

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Message-ID: <20241129084111.ifwak4y4irxjnpru@vireshk-i7>
Date: Fri, 29 Nov 2024 14:11:11 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Neil Armstrong <neil.armstrong@...aro.org>
Cc: Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
	Stephen Boyd <sboyd@...nel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] OPP: fix dev_pm_opp_find_bw_*() when bandwidth table
 not initialized

On 28-11-24, 11:07, Neil Armstrong wrote:
> If a driver calls dev_pm_opp_find_bw_ceil/floor() the retrieve bandwidth
> from the OPP table but the bandwidth table was not created because the
> interconnect properties were missing in the OPP consumer node, the
> kernel will crash with:
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000004
> ...
> pc : _read_bw+0x8/0x10
> lr : _opp_table_find_key+0x9c/0x174
> ...
> Call trace:
>   _read_bw+0x8/0x10 (P)
>   _opp_table_find_key+0x9c/0x174 (L)
>   _find_key+0x98/0x168
>   dev_pm_opp_find_bw_ceil+0x50/0x88
> ...
> 
> In order to fix the crash, create an assert function to check
> if the bandwidth table were created before trying to get a
> bandwidth with _read_bw().
> 
> Fixes: add1dc094a74 ("OPP: Use generic key finding helpers for bandwidth key")
> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
> ---
>  drivers/opp/core.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index 8692e8ce05b7c31a725ea3a7928f238c7a1d6f51..178780e294dad49c22d866930efb7b8b13ae2d61 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -114,6 +114,14 @@ static bool assert_clk_index(struct opp_table *opp_table, int index)
>  	return opp_table->clk_count > index;
>  }
>  
> +/*
> + * Returns true if bandwidth table is large enough to contain the bandwidth index.
> + */
> +static bool assert_bandwidth_index(struct opp_table *opp_table, int index)
> +{
> +	return opp_table->path_count > index;
> +}
> +
>  /**
>   * dev_pm_opp_get_bw() - Gets the bandwidth corresponding to an opp
>   * @opp:	opp for which bandwidth has to be returned for
> @@ -913,7 +921,8 @@ struct dev_pm_opp *dev_pm_opp_find_bw_ceil(struct device *dev, unsigned int *bw,
>  	unsigned long temp = *bw;
>  	struct dev_pm_opp *opp;
>  
> -	opp = _find_key_ceil(dev, &temp, index, true, _read_bw, NULL);
> +	opp = _find_key_ceil(dev, &temp, index, true, _read_bw,
> +			     assert_bandwidth_index);
>  	*bw = temp;
>  	return opp;
>  }
> @@ -944,7 +953,8 @@ struct dev_pm_opp *dev_pm_opp_find_bw_floor(struct device *dev,
>  	unsigned long temp = *bw;
>  	struct dev_pm_opp *opp;
>  
> -	opp = _find_key_floor(dev, &temp, index, true, _read_bw, NULL);
> +	opp = _find_key_floor(dev, &temp, index, true, _read_bw,
> +			      assert_bandwidth_index);
>  	*bw = temp;
>  	return opp;
>  }

Applied. Thanks.

-- 
viresh