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Subject: Re: [PATCH v2 2/2] iommu/tegra-smmu: Expend mutex protection range
To:     Nicolin Chen <nicoleotsuka@gmail.com>, thierry.reding@gmail.com,
        joro@8bytes.org
Cc:     vdumpa@nvidia.com, jonathanh@nvidia.com,
        linux-tegra@vger.kernel.org, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
References: <20200928235901.28337-1-nicoleotsuka@gmail.com>
 <20200928235901.28337-3-nicoleotsuka@gmail.com>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <692b51fa-7a3e-dee7-b628-7cb2d2dc188d@gmail.com>
Date:   Tue, 29 Sep 2020 03:17:58 +0300
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...
>  static bool tegra_smmu_capable(enum iommu_cap cap)
> @@ -420,17 +413,21 @@ static int tegra_smmu_as_prepare(struct tegra_smmu *smmu,
>  				 struct tegra_smmu_as *as)
>  {
>  	u32 value;
> -	int err;
> +	int err = 0;
> +
> +	mutex_lock(&smmu->lock);
>  
>  	if (as->use_count > 0) {
>  		as->use_count++;
> -		return 0;
> +		goto err_unlock;

This looks a bit odd because it's not a error condition. Perhaps should
be better to "goto bump_usecount"?

Or make it similar to tegra_smmu_as_unprepare()?

>  	}
>  
>  	as->pd_dma = dma_map_page(smmu->dev, as->pd, 0, SMMU_SIZE_PD,
>  				  DMA_TO_DEVICE);
> -	if (dma_mapping_error(smmu->dev, as->pd_dma))
> -		return -ENOMEM;
> +	if (dma_mapping_error(smmu->dev, as->pd_dma)) {
> +		err = -ENOMEM;
> +		goto err_unlock;
> +	}
>  
>  	/* We can't handle 64-bit DMA addresses */
>  	if (!smmu_dma_addr_valid(smmu, as->pd_dma)) {
> @@ -453,24 +450,35 @@ static int tegra_smmu_as_prepare(struct tegra_smmu *smmu,
>  	as->smmu = smmu;

bump_usecount:

>  	as->use_count++;
>  
> +	mutex_unlock(&smmu->lock);
> +
>  	return 0;
>  
>  err_unmap:
>  	dma_unmap_page(smmu->dev, as->pd_dma, SMMU_SIZE_PD, DMA_TO_DEVICE);
> +err_unlock:
> +	mutex_unlock(&smmu->lock);
> +
>  	return err;
>  }
>  
>  static void tegra_smmu_as_unprepare(struct tegra_smmu *smmu,
>  				    struct tegra_smmu_as *as)
>  {
> -	if (--as->use_count > 0)
> +	mutex_lock(&smmu->lock);
> +
> +	if (--as->use_count > 0) {
> +		mutex_unlock(&smmu->lock);
>  		return;
> +	}
>  
>  	tegra_smmu_free_asid(smmu, as->id);
>  
>  	dma_unmap_page(smmu->dev, as->pd_dma, SMMU_SIZE_PD, DMA_TO_DEVICE);
>  
>  	as->smmu = NULL;
> +
> +	mutex_unlock(&smmu->lock);
>  }
>  
>  static int tegra_smmu_attach_dev(struct iommu_domain *domain,
>