kernel: better document the use_mm/unuse_mm API contract

Switch the function documentation to kerneldoc comments, and add
WARN_ON_ONCE asserts that the calling thread is a kernel thread and does
not have ->mm set (or has ->mm set in the case of unuse_mm).

Also give the functions a kthread_ prefix to better document the use case.

[hch@lst.de: fix a comment typo, cover the newly merged use_mm/unuse_mm caller in vfio]
  Link: http://lkml.kernel.org/r/20200416053158.586887-3-hch@lst.de
[sfr@canb.auug.org.au: powerpc/vas: fix up for {un}use_mm() rename]
  Link: http://lkml.kernel.org/r/20200422163935.5aa93ba5@canb.auug.org.au

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> [usb]
Acked-by: Haren Myneni <haren@linux.ibm.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: Jason Wang <jasowang@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Link: http://lkml.kernel.org/r/20200404094101.672954-6-hch@lst.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 10 insertions, 10 deletions

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
index b94bbb8e7bb4..142746836838 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
@@ -197,9 +197,9 @@ uint8_t amdgpu_amdkfd_get_xgmi_hops_count(struct kgd_dev *dst, struct kgd_dev *s
 			if ((mmptr) == current->mm) {			\
 				valid = !get_user((dst), (wptr));	\
 			} else if (current->mm == NULL) {		\
-				use_mm(mmptr);				\
+				kthread_use_mm(mmptr);			\
 				valid = !get_user((dst), (wptr));	\
-				unuse_mm(mmptr);			\
+				kthread_unuse_mm(mmptr);		\
 			}						\
 			pagefault_enable();				\
 		}							\
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 7ae54b7b637b..f80b2747d7c5 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -827,9 +827,9 @@ static void ffs_user_copy_worker(struct work_struct *work)
 		mm_segment_t oldfs = get_fs();
 
 		set_fs(USER_DS);
-		use_mm(io_data->mm);
+		kthread_use_mm(io_data->mm);
 		ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);
-		unuse_mm(io_data->mm);
+		kthread_unuse_mm(io_data->mm);
 		set_fs(oldfs);
 	}
 
diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 20fba95ed0a6..9ee0bfe7bcda 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -462,9 +462,9 @@ static void ep_user_copy_worker(struct work_struct *work)
 	struct kiocb *iocb = priv->iocb;
 	size_t ret;
 
-	use_mm(mm);
+	kthread_use_mm(mm);
 	ret = copy_to_iter(priv->buf, priv->actual, &priv->to);
-	unuse_mm(mm);
+	kthread_unuse_mm(mm);
 	if (!ret)
 		ret = -EFAULT;
 
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index d5c08a750441..5e556ac9102a 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -2817,7 +2817,7 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
 		return -EPERM;
 
 	if (kthread)
-		use_mm(mm);
+		kthread_use_mm(mm);
 	else if (current->mm != mm)
 		goto out;
 
@@ -2844,7 +2844,7 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
 		*copied = copy_from_user(data, (void __user *)vaddr,
 					   count) ? 0 : count;
 	if (kthread)
-		unuse_mm(mm);
+		kthread_unuse_mm(mm);
 out:
 	mmput(mm);
 	return *copied ? 0 : -EFAULT;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index ffc7cc31d7eb..1ad3d10c121a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -332,7 +332,7 @@ static int vhost_worker(void *data)
 	mm_segment_t oldfs = get_fs();
 
 	set_fs(USER_DS);
-	use_mm(dev->mm);
+	kthread_use_mm(dev->mm);
 
 	for (;;) {
 		/* mb paired w/ kthread_stop */
@@ -360,7 +360,7 @@ static int vhost_worker(void *data)
 				schedule();
 		}
 	}
-	unuse_mm(dev->mm);
+	kthread_unuse_mm(dev->mm);
 	set_fs(oldfs);
 	return 0;
 }