mm: Rename SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU

A group of Linux kernel hackers reported chasing a bug that resulted
from their assumption that SLAB_DESTROY_BY_RCU provided an existence
guarantee, that is, that no block from such a slab would be reallocated
during an RCU read-side critical section.  Of course, that is not the
case.  Instead, SLAB_DESTROY_BY_RCU only prevents freeing of an entire
slab of blocks.

However, there is a phrase for this, namely "type safety".  This commit
therefore renames SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU in order
to avoid future instances of this sort of confusion.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.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: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
[ paulmck: Add comments mentioning the old name, as requested by Eric
  Dumazet, in order to help people familiar with the old name find
  the new one. ]
Acked-by: David Rientjes <rientjes@google.com>

1 files changed, 6 insertions, 6 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 7f4bc70..57e5156 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1687,7 +1687,7 @@ static void rcu_free_slab(struct rcu_head *h)
 
 static void free_slab(struct kmem_cache *s, struct page *page)
 {
-	if (unlikely(s->flags & SLAB_DESTROY_BY_RCU)) {
+	if (unlikely(s->flags & SLAB_TYPESAFE_BY_RCU)) {
 		struct rcu_head *head;
 
 		if (need_reserve_slab_rcu) {
@@ -2963,7 +2963,7 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page,
 	 * slab_free_freelist_hook() could have put the items into quarantine.
 	 * If so, no need to free them.
 	 */
-	if (s->flags & SLAB_KASAN && !(s->flags & SLAB_DESTROY_BY_RCU))
+	if (s->flags & SLAB_KASAN && !(s->flags & SLAB_TYPESAFE_BY_RCU))
 		return;
 	do_slab_free(s, page, head, tail, cnt, addr);
 }
@@ -3433,7 +3433,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
 	 * the slab may touch the object after free or before allocation
 	 * then we should never poison the object itself.
 	 */
-	if ((flags & SLAB_POISON) && !(flags & SLAB_DESTROY_BY_RCU) &&
+	if ((flags & SLAB_POISON) && !(flags & SLAB_TYPESAFE_BY_RCU) &&
 			!s->ctor)
 		s->flags |= __OBJECT_POISON;
 	else
@@ -3455,7 +3455,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
 	 */
 	s->inuse = size;
 
-	if (((flags & (SLAB_DESTROY_BY_RCU | SLAB_POISON)) ||
+	if (((flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) ||
 		s->ctor)) {
 		/*
 		 * Relocate free pointer after the object if it is not
@@ -3537,7 +3537,7 @@ static int kmem_cache_open(struct kmem_cache *s, unsigned long flags)
 	s->flags = kmem_cache_flags(s->size, flags, s->name, s->ctor);
 	s->reserved = 0;
 
-	if (need_reserve_slab_rcu && (s->flags & SLAB_DESTROY_BY_RCU))
+	if (need_reserve_slab_rcu && (s->flags & SLAB_TYPESAFE_BY_RCU))
 		s->reserved = sizeof(struct rcu_head);
 
 	if (!calculate_sizes(s, -1))
@@ -5042,7 +5042,7 @@ SLAB_ATTR_RO(cache_dma);
 
 static ssize_t destroy_by_rcu_show(struct kmem_cache *s, char *buf)
 {
-	return sprintf(buf, "%d\n", !!(s->flags & SLAB_DESTROY_BY_RCU));
+	return sprintf(buf, "%d\n", !!(s->flags & SLAB_TYPESAFE_BY_RCU));
 }
 SLAB_ATTR_RO(destroy_by_rcu);