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; 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); -- _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu