mm/slub: Remove the ULONG_MAX stack trace hackery

No architecture terminates the stack trace with ULONG_MAX anymore. Remove
the cruft.

While at it remove the pointless loop of clearing the stack array
completely. It's sufficient to clear the last entry as the consumers break
out on the first zeroed entry anyway.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: linux-mm@kvack.org
Cc: David Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Link: https://lkml.kernel.org/r/20190410103644.574058244@linutronix.de

mm/slub.c

@@ -553,7 +553,6 @@ static void set_track(struct kmem_cache *s, void *object,
 	if (addr) {
 #ifdef CONFIG_STACKTRACE
 		struct stack_trace trace;
-		int i;
 
 		trace.nr_entries = 0;
 		trace.max_entries = TRACK_ADDRS_COUNT;
@@ -563,20 +562,16 @@ static void set_track(struct kmem_cache *s, void *object,
 		save_stack_trace(&trace);
 		metadata_access_disable();
 
-		/* See rant in lockdep.c */
-		if (trace.nr_entries != 0 &&
-		    trace.entries[trace.nr_entries - 1] == ULONG_MAX)
-			trace.nr_entries--;
-
-		for (i = trace.nr_entries; i < TRACK_ADDRS_COUNT; i++)
-			p->addrs[i] = 0;
+		if (trace.nr_entries < TRACK_ADDRS_COUNT)
+			p->addrs[trace.nr_entries] = 0;
 #endif
 		p->addr = addr;
 		p->cpu = smp_processor_id();
 		p->pid = current->pid;
 		p->when = jiffies;
-	} else
+	} else {
 		memset(p, 0, sizeof(struct track));
+	}
 }
 
 static void init_tracking(struct kmem_cache *s, void *object)