IB/uverbs: Export ib_umem_get()/ib_umem_release() to modules

Export ib_umem_get()/ib_umem_release() and put low-level drivers in
control of when to call ib_umem_get() to pin and DMA map userspace,
rather than always calling it in ib_uverbs_reg_mr() before calling the
low-level driver's reg_user_mr method.

Also move these functions to be in the ib_core module instead of
ib_uverbs, so that driver modules using them do not depend on
ib_uverbs.

This has a number of advantages:
 - It is better design from the standpoint of making generic code a
   library that can be used or overridden by device-specific code as
   the details of specific devices dictate.
 - Drivers that do not need to pin userspace memory regions do not
   need to take the performance hit of calling ib_mem_get().  For
   example, although I have not tried to implement it in this patch,
   the ipath driver should be able to avoid pinning memory and just
   use copy_{to,from}_user() to access userspace memory regions.
 - Buffers that need special mapping treatment can be identified by
   the low-level driver.  For example, it may be possible to solve
   some Altix-specific memory ordering issues with mthca CQs in
   userspace by mapping CQ buffers with extra flags.
 - Drivers that need to pin and DMA map userspace memory for things
   other than memory regions can use ib_umem_get() directly, instead
   of hacks using extra parameters to their reg_phys_mr method.  For
   example, the mlx4 driver that is pending being merged needs to pin
   and DMA map QP and CQ buffers, but it does not need to create a
   memory key for these buffers.  So the cleanest solution is for mlx4
   to call ib_umem_get() in the create_qp and create_cq methods.

Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/core/uverbs_main.c

@@ -183,6 +183,8 @@ static int ib_uverbs_cleanup_ucontext(struct ib_uverbs_file *file,
 	if (!context)
 		return 0;
 
+	context->closing = 1;
+
 	list_for_each_entry_safe(uobj, tmp, &context->ah_list, list) {
 		struct ib_ah *ah = uobj->object;
 
@@ -230,16 +232,10 @@ static int ib_uverbs_cleanup_ucontext(struct ib_uverbs_file *file,
 
 	list_for_each_entry_safe(uobj, tmp, &context->mr_list, list) {
 		struct ib_mr *mr = uobj->object;
-		struct ib_device *mrdev = mr->device;
-		struct ib_umem_object *memobj;
 
 		idr_remove_uobj(&ib_uverbs_mr_idr, uobj);
 		ib_dereg_mr(mr);
-
-		memobj = container_of(uobj, struct ib_umem_object, uobject);
-		ib_umem_release_on_close(mrdev, &memobj->umem);
-
-		kfree(memobj);
+		kfree(uobj);
 	}
 
 	list_for_each_entry_safe(uobj, tmp, &context->pd_list, list) {
@@ -906,7 +902,6 @@ static void __exit ib_uverbs_cleanup(void)
 	unregister_filesystem(&uverbs_event_fs);
 	class_destroy(uverbs_class);
 	unregister_chrdev_region(IB_UVERBS_BASE_DEV, IB_UVERBS_MAX_DEVICES);
-	flush_scheduled_work();
 	idr_destroy(&ib_uverbs_pd_idr);
 	idr_destroy(&ib_uverbs_mr_idr);
 	idr_destroy(&ib_uverbs_mw_idr);