linux-kernel - Re: [PATCH] drm/amd/pm: avoid large variable on kernel stack

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Date:   Thu, 15 Dec 2022 20:46:02 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     arnd@...nel.org
Cc:     Hawking.Zhang@....com, Jack.Gui@....com, KevinYang.Wang@....com,
        Xinhui.Pan@....com, airlied@...il.com, alexander.deucher@....com,
        amd-gfx@...ts.freedesktop.org, arnd@...db.de,
        christian.koenig@....com, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, evan.quan@....com,
        kenneth.feng@....com, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, nathan@...nel.org, ndesaulniers@...gle.com,
        trix@...hat.com
Subject: Re: [PATCH] drm/amd/pm: avoid large variable on kernel stack

Le 15/12/2022 à 17:36, Arnd Bergmann a écrit :
> From: Arnd Bergmann <arnd-r2nGTMty4D4@...lic.gmane.org>
> 
> The activity_monitor_external[] array is too big to fit on the
> kernel stack, resulting in this warning with clang:
> 
> drivers/gpu/drm/amd/amdgpu/../pm/swsmu/smu13/smu_v13_0_7_ppt.c:1438:12: error: stack frame size (1040) exceeds limit (1024) in 'smu_v13_0_7_get_power_profile_mode' [-Werror,-Wframe-larger-than]
> 
> Use dynamic allocation instead. It should also be possible to
> have single element here instead of the array, but this seems
> easier.
> 
> Fixes: 334682ae8151 ("drm/amd/pm: enable workload type change on smu_v13_0_7")
> Signed-off-by: Arnd Bergmann <arnd-r2nGTMty4D4@...lic.gmane.org>
> ---
>   .../drm/amd/pm/swsmu/smu13/smu_v13_0_7_ppt.c  | 21 ++++++++++++++-----
>   1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/pm/swsmu/smu13/smu_v13_0_7_ppt.c b/drivers/gpu/drm/amd/pm/swsmu/smu13/smu_v13_0_7_ppt.c
> index c270f94a1b86..7eba854e09ec 100644
> --- a/drivers/gpu/drm/amd/pm/swsmu/smu13/smu_v13_0_7_ppt.c
> +++ b/drivers/gpu/drm/amd/pm/swsmu/smu13/smu_v13_0_7_ppt.c
> @@ -1439,7 +1439,7 @@ static int smu_v13_0_7_get_power_limit(struct smu_context *smu,
>   
>   static int smu_v13_0_7_get_power_profile_mode(struct smu_context *smu, char *buf)
>   {
> -	DpmActivityMonitorCoeffIntExternal_t activity_monitor_external[PP_SMC_POWER_PROFILE_COUNT];
> +	DpmActivityMonitorCoeffIntExternal_t *activity_monitor_external;
>   	uint32_t i, j, size = 0;
>   	int16_t workload_type = 0;
>   	int result = 0;
> @@ -1447,6 +1447,12 @@ static int smu_v13_0_7_get_power_profile_mode(struct smu_context *smu, char *buf
>   	if (!buf)
>   		return -EINVAL;
>   
> +	activity_monitor_external = kcalloc(sizeof(activity_monitor_external),

Hi,

Before, 'activity_monitor_external' was not initialized.
Maybe kcalloc() is enough?

sizeof(*activity_monitor_external)?
      ~~~~

> +					    PP_SMC_POWER_PROFILE_COUNT,
> +					    GFP_KERNEL);
> +	if (!activity_monitor_external)
> +		return -ENOMEM;
> +
>   	size += sysfs_emit_at(buf, size, "                              ");
>   	for (i = 0; i <= PP_SMC_POWER_PROFILE_WINDOW3D; i++)

Unrelated, but wouldn't it be more straightforward with "< 
PP_SMC_POWER_PROFILE_COUNT"?

>   		size += sysfs_emit_at(buf, size, "%-14s%s", amdgpu_pp_profile_name[i],
> @@ -1459,15 +1465,17 @@ static int smu_v13_0_7_get_power_profile_mode(struct smu_context *smu, char *buf
>   		workload_type = smu_cmn_to_asic_specific_index(smu,
>   							       CMN2ASIC_MAPPING_WORKLOAD,
>   							       i);
> -		if (workload_type < 0)
> -			return -EINVAL;
> +		if (workload_type < 0) {
> +			result = -EINVAL;
> +			goto out;
> +		}
>   
>   		result = smu_cmn_update_table(smu,
>   					  SMU_TABLE_ACTIVITY_MONITOR_COEFF, workload_type,
>   					  (void *)(&activity_monitor_external[i]), false);
>   		if (result) {
>   			dev_err(smu->adev->dev, "[%s] Failed to get activity monitor!", __func__);
> -			return result;
> +			goto out;
>   		}
>   	}
>   
> @@ -1495,7 +1503,10 @@ do {													\
>   	PRINT_DPM_MONITOR(Fclk_BoosterFreq);
>   #undef PRINT_DPM_MONITOR
>   
> -	return size;
> +	result = size;
> +out:
> +	kfree(activity_monitor_external);
> +	return result;
>   }
>   
>   static int smu_v13_0_7_set_power_profile_mode(struct smu_context *smu, long *input, uint32_t size)