slab: make GFP_SLAB_BUG_MASK information more human readable

printk offers %pGg for quite some time so let's use it to get a human
readable list of invalid flags.

The original output would be
  [  429.191962] gfp: 2

after the change
  [  429.191962] Unexpected gfp: 0x2 (__GFP_HIGHMEM)

Link: http://lkml.kernel.org/r/1465548200-11384-1-git-send-email-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.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/slab.c

@@ -2686,7 +2686,8 @@ static struct page *cache_grow_begin(struct kmem_cache *cachep,
 	 * critical path in kmem_cache_alloc().
 	 */
 	if (unlikely(flags & GFP_SLAB_BUG_MASK)) {
-		pr_emerg("gfp: %u\n", flags & GFP_SLAB_BUG_MASK);
+		gfp_t invalid_mask = flags & GFP_SLAB_BUG_MASK;
+		pr_emerg("Unexpected gfp: %#x (%pGg)\n", invalid_mask, &invalid_mask);
 		BUG();
 	}
 	local_flags = flags & (GFP_CONSTRAINT_MASK|GFP_RECLAIM_MASK);

mm/slub.c

@@ -1612,7 +1612,8 @@ out:
 static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
 {
 	if (unlikely(flags & GFP_SLAB_BUG_MASK)) {
-		pr_emerg("gfp: %u\n", flags & GFP_SLAB_BUG_MASK);
+		gfp_t invalid_mask = flags & GFP_SLAB_BUG_MASK;
+		pr_emerg("Unexpected gfp: %#x (%pGg)\n", invalid_mask, &invalid_mask);
 		BUG();
 	}