SLUB: fix behavior if the text output of list_locations overflows PAGE_SIZE

If slabs are allocated or freed from a large set of call sites (typical for
the kmalloc area) then we may create more output than fits into a single
PAGE and sysfs only gives us one page.  The output should be truncated.
This patch fixes the checks to do the truncation properly.
Signed-off-by: NChristoph Lameter <clameter@sgi.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -3042,13 +3042,15 @@ static int list_locations(struct kmem_cache *s, char *buf,
 			n += sprintf(buf + n, " pid=%ld",
 				l->min_pid);
 
-		if (num_online_cpus() > 1 && !cpus_empty(l->cpus)) {
+		if (num_online_cpus() > 1 && !cpus_empty(l->cpus) &&
+				n < PAGE_SIZE - 60) {
 			n += sprintf(buf + n, " cpus=");
 			n += cpulist_scnprintf(buf + n, PAGE_SIZE - n - 50,
 					l->cpus);
 		}
 
-		if (num_online_nodes() > 1 && !nodes_empty(l->nodes)) {
+		if (num_online_nodes() > 1 && !nodes_empty(l->nodes) &&
+				n < PAGE_SIZE - 60) {
 			n += sprintf(buf + n, " nodes=");
 			n += nodelist_scnprintf(buf + n, PAGE_SIZE - n - 50,
 					l->nodes);