diff mbox series

[v2,2/2] iommu/tegra-smmu: Expend mutex protection range

Message ID 20200928235901.28337-3-nicoleotsuka@gmail.com
State New
Headers show
Series iommu/tegra-smmu: Two followup changes | expand

Commit Message

Nicolin Chen Sept. 28, 2020, 11:59 p.m. UTC
This is used to protect potential race condition at use_count.
since probes of client drivers, calling attach_dev(), may run
concurrently.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
---

Changelog
v1->v2:
 * N/A

 drivers/iommu/tegra-smmu.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

Comments

Dmitry Osipenko Sept. 29, 2020, 12:17 a.m. UTC | #1
...
>  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,
>
Nicolin Chen Sept. 29, 2020, 1:15 a.m. UTC | #2
On Tue, Sep 29, 2020 at 03:17:58AM +0300, Dmitry Osipenko wrote:
> ...
> >  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()?

Hmm...I think it's simple to just make it "goto unlock" then.
diff mbox series

Patch

diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
index ec4c9dafff95..acda5902e095 100644
--- a/drivers/iommu/tegra-smmu.c
+++ b/drivers/iommu/tegra-smmu.c
@@ -256,26 +256,19 @@  static int tegra_smmu_alloc_asid(struct tegra_smmu *smmu, unsigned int *idp)
 {
 	unsigned long id;
 
-	mutex_lock(&smmu->lock);
-
 	id = find_first_zero_bit(smmu->asids, smmu->soc->num_asids);
-	if (id >= smmu->soc->num_asids) {
-		mutex_unlock(&smmu->lock);
+	if (id >= smmu->soc->num_asids)
 		return -ENOSPC;
-	}
 
 	set_bit(id, smmu->asids);
 	*idp = id;
 
-	mutex_unlock(&smmu->lock);
 	return 0;
 }
 
 static void tegra_smmu_free_asid(struct tegra_smmu *smmu, unsigned int id)
 {
-	mutex_lock(&smmu->lock);
 	clear_bit(id, smmu->asids);
-	mutex_unlock(&smmu->lock);
 }
 
 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;
 	}
 
 	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;
 	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,