On Mon, 6 Jul 2020 16:04:13 +0200 Markus Elfring wrote:
>
> Can another design approach make sense here?
>
> + bool thread_use_mm = ((current->flags & PF_KTHREAD) && !current->mm);
> + if (thread_use_mm)
Good. See below.
>
>
> > kthread_use_mm(mm);
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -2798,7 +2798,7 @@ static int vfio_iommu_type1_dma_rw_chunk
struct mm_struct *mm;
unsigned long vaddr;
struct vfio_dma *dma;
- bool kthread = current->mm == NULL;
+ bool kthread_load_mm;
size_t offset;
*copied = 0;
@@ -2812,11 +2812,12 @@ static int vfio_iommu_type1_dma_rw_chunk
return -EPERM;
mm = get_task_mm(dma->task);
-
if (!mm)
return -EPERM;
- if (kthread)
+ kthread_load_mm = current->flags & PF_KTHREAD &&
+ current->mm == NULL;
+ if (kthread_load_mm)
kthread_use_mm(mm);
else if (current->mm != mm)
goto out;
@@ -2843,7 +2844,7 @@ static int vfio_iommu_type1_dma_rw_chunk
} else
*copied = copy_from_user(data, (void __user *)vaddr,
count) ? 0 : count;
- if (kthread)
+ if (kthread_load_mm)
kthread_unuse_mm(mm);
out:
mmput(mm);
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