mm/cma.c: warn if the CMA area could not be activated

While activating a CMA area we check to make sure that all the PFNs in
the range are inside the same zone.  This is a requirement for
alloc_contig_range() to work.  Any CMA area failing the check is
disabled for good.  This happens silently right now making all future
cma_alloc() allocations failure inevitable.

Here we add an error message stating that the CMA area could not be
activated which makes it easier to explain any future cma_alloc()
failures on it.  While in there, change the bail out goto label from
'err' to 'not_in_zone' which makes more sense.

Link: http://lkml.kernel.org/r/20170605023729.26303-1-khandual@linux.vnet.ibm.com
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/cma.c

@@ -127,7 +127,7 @@ static int __init cma_activate_area(struct cma *cma)
 			 * to be in the same zone.
 			 */
 			if (page_zone(pfn_to_page(pfn)) != zone)
-				goto err;
+				goto not_in_zone;
 		}
 		init_cma_reserved_pageblock(pfn_to_page(base_pfn));
 	} while (--i);
@@ -141,7 +141,8 @@ static int __init cma_activate_area(struct cma *cma)
 
 	return 0;
 
-err:
+not_in_zone:
+	pr_err("CMA area %s could not be activated\n", cma->name);
 	kfree(cma->bitmap);
 	cma->count = 0;
 	return -EINVAL;