slub: disable tracing and failslab for merged slabs

Tracing of mergeable slabs as well as uses of failslab are confusing since
the objects of multiple slab caches will be affected.  Moreover this
creates a situation where a mergeable slab will become unmergeable.

If tracing or failslab testing is desired then it may be best to switch
merging off for starters.

Signed-off-by: Christoph Lameter <cl@linux.com>
Tested-by: WANG Chao <chaowang@redhat.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>

diff --git a/mm/slub.c b/mm/slub.c
index 3e8afcc07a760c552135cfb3c79ac924ee9e5494..fa86e58450935dc972a805ee932ed2dfc5e956db 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4604,6 +4604,14 @@ static ssize_t trace_show(struct kmem_cache *s, char *buf)
 static ssize_t trace_store(struct kmem_cache *s, const char *buf,
                                                        size_t length)
 {
+       /*
+        * Tracing a merged cache is going to give confusing results
+        * as well as cause other issues like converting a mergeable
+        * cache into an umergeable one.
+        */
+       if (s->refcount > 1)
+               return -EINVAL;
+
        s->flags &= ~SLAB_TRACE;
        if (buf[0] == '1') {
                s->flags &= ~__CMPXCHG_DOUBLE;
@@ -4721,6 +4729,9 @@ static ssize_t failslab_show(struct kmem_cache *s, char *buf)
 static ssize_t failslab_store(struct kmem_cache *s, const char *buf,
                                                        size_t length)
 {
+       if (s->refcount > 1)
+               return -EINVAL;
+
        s->flags &= ~SLAB_FAILSLAB;
        if (buf[0] == '1')
                s->flags |= SLAB_FAILSLAB;