On Mon, Jul 06, 2020 at 06:49:15PM +0800, Hillf Danton wrote:
>
> 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 <yan.y.z...@intel.com>
> Cc: Markus Elfring <markus.elfr...@web.de>
> Cc: Christoph Hellwig <h...@lst.de>
> Signed-off-by: Hillf Danton <hdan...@sina.com>
> ---
>
> --- 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;
is it acceptable to just rename "kthread" to "kthread_no_use_mm"?
I think "current->mm == NULL" in itself implies kthread and not use_mm,
as a user thread is not able to have "current->mm == NULL", right?
Thanks
Yan
> 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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