mm/slub.c: use jitter-free reference while printing age

When SLUB_DEBUG catches some issues, it prints all the required debug
info.  However, in a few cases where allocation and free of the object
has happened in a very short time, 'age' might be misleading.  See the
example below:

  =============================================================================
  BUG kmalloc-256 (Tainted: G        W  O   ): Poison overwritten
  -----------------------------------------------------------------------------
  ...
  INFO: Allocated in binder_transaction+0x4b0/0x2448 age=731 cpu=3 pid=5314
  ...
  INFO: Freed in binder_free_transaction+0x2c/0x58 age=735 cpu=6 pid=2079
  ...
  Object fffffff14956a870: 6b 6b 6b 6b 6b 6b 6b 6b 67 6b 6b 6b 6b 6b 6b a5  kkkkkkkkgkkkk

In this case, object got freed later but 'age' shows otherwise.  This
could be because, while printing this info, we print allocation traces
first and free traces thereafter.  In between, if we get schedule out or
jiffies increment, (jiffies - t->when) could become meaningless.

Use the jitter free reference to calculate age.

New output will exactly be same.  'age' is still staying with single
jiffies ref in both prints.

Change-Id: I0846565807a4229748649bbecb1ffb743d71fcd8
Link: http://lkml.kernel.org/r/1520492010-19389-1-git-send-email-cpandya@codeaurora.org
Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>
Acked-by: Christoph Lameter <cl@linux.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
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/slub.c

@@ -598,13 +598,13 @@ static void init_tracking(struct kmem_cache *s, void *object)
 	set_track(s, object, TRACK_ALLOC, 0UL);
 }
 
-static void print_track(const char *s, struct track *t)
+static void print_track(const char *s, struct track *t, unsigned long pr_time)
 {
 	if (!t->addr)
 		return;
 
 	pr_err("INFO: %s in %pS age=%lu cpu=%u pid=%d\n",
-	       s, (void *)t->addr, jiffies - t->when, t->cpu, t->pid);
+	       s, (void *)t->addr, pr_time - t->when, t->cpu, t->pid);
 #ifdef CONFIG_STACKTRACE
 	{
 		int i;
@@ -619,11 +619,12 @@ static void print_track(const char *s, struct track *t)
 
 static void print_tracking(struct kmem_cache *s, void *object)
 {
+	unsigned long pr_time = jiffies;
 	if (!(s->flags & SLAB_STORE_USER))
 		return;
 
-	print_track("Allocated", get_track(s, object, TRACK_ALLOC));
-	print_track("Freed", get_track(s, object, TRACK_FREE));
+	print_track("Allocated", get_track(s, object, TRACK_ALLOC), pr_time);
+	print_track("Freed", get_track(s, object, TRACK_FREE), pr_time);
 }
 
 static void print_page_info(struct page *page)