[patch 04/15] mm: emit the "free" trace report before freeing memory in kmem_cache_free()

[Andrew Morton <akpm@linux-foundation.org>]

From: Yunfeng Ye <yeyunfeng@huawei.com>
Subject: mm: emit the "free" trace report before freeing memory in kmem_cache_free()

After the memory is freed, it can be immediately allocated by other CPUs,
before the "free" trace report has been emitted.  This causes inaccurate
traces.

For example, if the following sequence of events occurs:

    CPU 0                 CPU 1

  (1) alloc xxxxxx
  (2) free  xxxxxx
                         (3) alloc xxxxxx
                         (4) free  xxxxxx

Then they will be inaccurately reported via tracing, so that they appear
to have happened in this order:

    CPU 0                 CPU 1

  (1) alloc xxxxxx
                         (2) alloc xxxxxx
  (3) free  xxxxxx
                         (4) free  xxxxxx

This makes it look like CPU 1 somehow managed to allocate memory that CPU
0 still had allocated for itself.

In order to avoid this, emit the "free xxxxxx" tracing report just before
the actual call to free the memory, instead of just after it.

Link: https://lkml.kernel.org/r/374eb75d-7404-8721-4e1e-65b0e5b17279@huawei.com
Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: John Hubbard <jhubbard@nvidia.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>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/slab.c |    3 +--
 mm/slob.c |    3 +--
 mm/slub.c |    2 +-
 3 files changed, 3 insertions(+), 5 deletions(-)

--- a/mm/slab.c~mm-emit-the-free-trace-report-before-freeing-memory-in-kmem_cache_free
+++ a/mm/slab.c
@@ -3733,14 +3733,13 @@ void kmem_cache_free(struct kmem_cache *
 	if (!cachep)
 		return;
 
+	trace_kmem_cache_free(_RET_IP_, objp, cachep->name);
 	local_irq_save(flags);
 	debug_check_no_locks_freed(objp, cachep->object_size);
 	if (!(cachep->flags & SLAB_DEBUG_OBJECTS))
 		debug_check_no_obj_freed(objp, cachep->object_size);
 	__cache_free(cachep, objp, _RET_IP_);
 	local_irq_restore(flags);
-
-	trace_kmem_cache_free(_RET_IP_, objp, cachep->name);
 }
 EXPORT_SYMBOL(kmem_cache_free);
 
--- a/mm/slob.c~mm-emit-the-free-trace-report-before-freeing-memory-in-kmem_cache_free
+++ a/mm/slob.c
@@ -666,6 +666,7 @@ static void kmem_rcu_free(struct rcu_hea
 void kmem_cache_free(struct kmem_cache *c, void *b)
 {
 	kmemleak_free_recursive(b, c->flags);
+	trace_kmem_cache_free(_RET_IP_, b, c->name);
 	if (unlikely(c->flags & SLAB_TYPESAFE_BY_RCU)) {
 		struct slob_rcu *slob_rcu;
 		slob_rcu = b + (c->size - sizeof(struct slob_rcu));
@@ -674,8 +675,6 @@ void kmem_cache_free(struct kmem_cache *
 	} else {
 		__kmem_cache_free(b, c->size);
 	}
-
-	trace_kmem_cache_free(_RET_IP_, b, c->name);
 }
 EXPORT_SYMBOL(kmem_cache_free);
 
--- a/mm/slub.c~mm-emit-the-free-trace-report-before-freeing-memory-in-kmem_cache_free
+++ a/mm/slub.c
@@ -3526,8 +3526,8 @@ void kmem_cache_free(struct kmem_cache *
 	s = cache_from_obj(s, x);
 	if (!s)
 		return;
-	slab_free(s, virt_to_head_page(x), x, NULL, 1, _RET_IP_);
 	trace_kmem_cache_free(_RET_IP_, x, s->name);
+	slab_free(s, virt_to_head_page(x), x, NULL, 1, _RET_IP_);
 }
 EXPORT_SYMBOL(kmem_cache_free);
 
_