mm/kasan: support non-blocking GFP in kasan_populate_vmalloc()

A "gfp_mask" is already passed to kasan_populate_vmalloc() as an argument
to respect GFPs from callers and KASAN uses it for its internal
allocations.

But apply_to_page_range() function ignores GFP flags due to a hard-coded
mask.

Wrap the call with memalloc_apply_gfp_scope()/memalloc_restore_scope() so
that non-blocking GFP flags(GFP_ATOMIC, GFP_NOWAIT) are respected.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Uladzislau Rezki (Sony) <[e-mail]>
Reviewed-by: Baoquan He <[e-mail]>
Reviewed-by: Andrey Ryabinin <[e-mail]>
Cc: Alexander Potapenko <[e-mail]>
Cc: Marco Elver <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/kasan/shadow.c

···
 		 * page tables allocations ignore external gfp mask, enforce it
 		 * by the scope API
 		 */
-		if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
-			flags = memalloc_nofs_save();
-		else if ((gfp_mask & (__GFP_FS | __GFP_IO)) == 0)
-			flags = memalloc_noio_save();
-
+		flags = memalloc_apply_gfp_scope(gfp_mask);
 		ret = apply_to_page_range(&init_mm, start, nr_pages * PAGE_SIZE,
 					  kasan_populate_vmalloc_pte, &data);
-
-		if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
-			memalloc_nofs_restore(flags);
-		else if ((gfp_mask & (__GFP_FS | __GFP_IO)) == 0)
-			memalloc_noio_restore(flags);
+		memalloc_restore_scope(flags);
 
 		___free_pages_bulk(data.pages, nr_pages);
 		if (ret)