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 <[email protected]>
---
Changelog
v1->v2:
* N/A
drivers/iommu/tegra-smmu.c | 34 +++++++++++++++++++++-------------
1 file changed, 21 insertions(+), 13 deletions(-)
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,
--
2.17.1
...
> 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,
>
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.