Re: [PATCH 3/3] iommu/vt-d: Simplify domain_attach_iommu()

[Baolu Lu]

On 4/26/25 02:49, Dan Williams wrote:
> Lu Baolu wrote:
> > Use the __free(kfree) attribute with kzalloc() to automatically handle
> > the freeing of the allocated struct iommu_domain_info on error or early
> > exit paths, eliminating the need for explicit kfree() calls in error
> > handling branches.
> >
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.c | 29 ++++++++---------------------
> >   1 file changed, 8 insertions(+), 21 deletions(-)
> >
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 3a9ea0ad2cd3..12382c85495f 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -1337,13 +1337,14 @@ static bool first_level_by_default(struct intel_iommu *iommu)
> >   
> >   int domain_attach_iommu(struct dmar_domain *domain, struct intel_iommu *iommu)
> >   {
> > -	struct iommu_domain_info *info, *curr;
> > -	int num, ret = -ENOSPC;
> > +	struct iommu_domain_info *curr;
> > +	int num;
> >   
> >   	if (domain->domain.type == IOMMU_DOMAIN_SVA)
> >   		return 0;
> >   
> > -	info = kzalloc(sizeof(*info), GFP_KERNEL);
> > +	struct iommu_domain_info *info __free(kfree) =
> > +		kzalloc(sizeof(*info), GFP_KERNEL);
> >   	if (!info)
> >   		return -ENOMEM;
> >   
> > @@ -1351,34 +1352,20 @@ int domain_attach_iommu(struct dmar_domain *domain, struct intel_iommu *iommu)
> [..]
> > -err_clear:
> > -	ida_free(&iommu->domain_ida, info->did);
> > -err_unlock:
> > -	kfree(info);
> > -	return ret;
> > +	return xa_err(xa_store(&domain->iommu_array, iommu->seq_id,
> > +			       no_free_ptr(info), GFP_KERNEL));
> >   }
>
> This pattern looks like it wants a "xa_store_or_{reset,kfree}()" helper that
> handles both canceling a scope based cleanup and taking responsibility for
> error-exit-freeing @info in one statement.
>
> I.e. this is similar to a:
>
> 	"return devm_add_action_or_reset(..., no_free_ptr(obj), ...)"
>
> ...pattern.

Yes. Perhaps adding a xa_store variant would be beneficial in all
places that require this pattern.

Something like this?

diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 78eede109b1a..efbdff7ebda4 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -626,6 +626,35 @@ static inline void *xa_store_irq(struct xarray *xa, 
unsigned long index,
        return curr;
 }

+/**
+ * xa_store_or_kfree() - Store this entry in the XArray.
+ * @xa: XArray.
+ * @index: Index into array.
+ * @entry: New entry.
+ * @gfp: Memory allocation flags.
+ *
+ * This function is like calling xa_store() except it kfrees the new
+ * entry if an error happened.
+ *
+ * Context: Process context. Any context. Takes and releases the xa_lock.
+ * May sleep if the @gfp flags permit.
+ * Return: The old entry at this index or xa_err() if an error happened.
+ */
+static inline void *xa_store_or_kfree(struct xarray *xa, unsigned long 
index,
+               void *entry, gfp_t gfp)
+{
+       void *curr;
+
+       xa_lock(xa);
+       curr = __xa_store(xa, index, entry, gfp);
+       xa_unlock(xa);
+
+       if (xa_err(curr))
+               kfree(entry);
+
+       return curr;
+}
+
 /**
  * xa_erase_bh() - Erase this entry from the XArray.
  * @xa: XArray.

Thanks,
baolu