vmalloc: export __vmalloc_node_range for CONFIG_TEST_VMALLOC_MODULE

Export __vmaloc_node_range() function if CONFIG_TEST_VMALLOC_MODULE is
enabled.  Some test cases in vmalloc test suite module require and make
use of that function.  Please note, that it is not supposed to be used
for other purposes.

We need it only for performance analysis, stressing and stability check
of vmalloc allocator.

Link: http://lkml.kernel.org/r/20190103142108.20744-2-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmalloc.c

@@ -1774,6 +1774,15 @@ fail:
 	return NULL;
 }
 
+/*
+ * This is only for performance analysis of vmalloc and stress purpose.
+ * It is required by vmalloc test module, therefore do not use it other
+ * than that.
+ */
+#ifdef CONFIG_TEST_VMALLOC_MODULE
+EXPORT_SYMBOL_GPL(__vmalloc_node_range);
+#endif
+
 /**
  *	__vmalloc_node  -  allocate virtually contiguous memory
  *	@size:		allocation size