It's incorrect to tell out if a task is kthread without checking
PF_KTHREAD at all.
What's also fixed, if no need to be in a seperate patch, is to
invoke kthread_use_mm() without checking the current mm first as
the kthread may hold a mm struct atm and it's not the right place
to switch mm.
Fixes: 8d46c0cca5f4 ("vfio: introduce vfio_dma_rw to read/write a range of
IOVAs")
Cc: Yan Zhao <[email protected]>
Cc: Markus Elfring <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Signed-off-by: Hillf Danton <[email protected]>
---
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -2798,7 +2798,8 @@ 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 = current->flags & PF_KTHREAD;
+ bool use_mm = current->mm == NULL;
size_t offset;
*copied = 0;
@@ -2812,11 +2813,10 @@ static int vfio_iommu_type1_dma_rw_chunk
return -EPERM;
mm = get_task_mm(dma->task);
-
if (!mm)
return -EPERM;
- if (kthread)
+ if (kthread && use_mm)
kthread_use_mm(mm);
else if (current->mm != mm)
goto out;
@@ -2843,7 +2843,7 @@ static int vfio_iommu_type1_dma_rw_chunk
} else
*copied = copy_from_user(data, (void __user *)vaddr,
count) ? 0 : count;
- if (kthread)
+ if (kthread && use_mm)
kthread_unuse_mm(mm);
out:
mmput(mm);
--
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