[PATCH v3] slab: Ignore internal flags in cache creation

[Glauber Costa]

Some flags are used internally by the allocators for management
purposes. One example of that is the CFLGS_OFF_SLAB flag that slab uses
to mark that the metadata for that cache is stored outside of the slab.

No cache should ever pass those as a creation flags. We can just ignore
this bit if it happens to be passed (such as when duplicating a cache in
the kmem memcg patches).

Because such flags can vary from allocator to allocator, we allow them
to make their own decisions on that, defining SLAB_AVAILABLE_FLAGS with
all flags that are valid at creation time.  Allocators that doesn't have
any specific flag requirement should define that to mean all flags.

Common code will mask out all flags not belonging to that set.

[ v2: leave the mask out decision up to the allocators ]
[ v3: define flags for all allocators ]

Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
Acked-by: Christoph Lameter <cl@xxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
CC: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
---
 include/linux/slab_def.h | 19 +++++++++++++++++++
 include/linux/slob_def.h |  2 ++
 include/linux/slub_def.h |  2 ++
 mm/slab.c                | 22 ----------------------
 mm/slab_common.c         |  7 +++++++
 5 files changed, 30 insertions(+), 22 deletions(-)

diff --git a/include/linux/slab_def.h b/include/linux/slab_def.h
index 36d7031..cec4f5d 100644
--- a/include/linux/slab_def.h
+++ b/include/linux/slab_def.h
@@ -15,6 +15,25 @@
 #include <asm/cache.h>		/* kmalloc_sizes.h needs L1_CACHE_BYTES */
 #include <linux/compiler.h>
 
+/* Legal flag mask for kmem_cache_create(). */
+#ifdef CONFIG_DEBUG_SLAB 
+#define SLAB_AVAILABLE_FLAGS (SLAB_RED_ZONE | 				\
+			SLAB_POISON | SLAB_HWCACHE_ALIGN | 		\
+			SLAB_CACHE_DMA | 				\
+			SLAB_STORE_USER | 				\
+			SLAB_RECLAIM_ACCOUNT | SLAB_PANIC | 		\
+			SLAB_DESTROY_BY_RCU | SLAB_MEM_SPREAD | 	\
+			SLAB_DEBUG_OBJECTS | SLAB_NOLEAKTRACE |	\
+			SLAB_NOTRACK)
+#else
+#define SLAB_AVAILABLE_FLAGS (SLAB_HWCACHE_ALIGN | 			\
+			SLAB_CACHE_DMA | 				\
+			SLAB_RECLAIM_ACCOUNT | SLAB_PANIC | 		\
+			SLAB_DESTROY_BY_RCU | SLAB_MEM_SPREAD | 	\
+			SLAB_DEBUG_OBJECTS | SLAB_NOLEAKTRACE | 	\
+			SLAB_NOTRACK)
+#endif
+
 /*
  * struct kmem_cache
  *
diff --git a/include/linux/slob_def.h b/include/linux/slob_def.h
index 0ec00b3..606b97b 100644
--- a/include/linux/slob_def.h
+++ b/include/linux/slob_def.h
@@ -1,6 +1,8 @@
 #ifndef __LINUX_SLOB_DEF_H
 #define __LINUX_SLOB_DEF_H
 
+#define SLAB_AVAILABLE_FLAGS	0xFFFFFFFFUL /* No flag restriction */
+
 void *kmem_cache_alloc_node(struct kmem_cache *, gfp_t flags, int node);
 
 static __always_inline void *kmem_cache_alloc(struct kmem_cache *cachep,
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index df448ad..9e9b8c5 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -14,6 +14,8 @@
 
 #include <linux/kmemleak.h>
 
+#define SLAB_AVAILABLE_FLAGS	0xFFFFFFFFUL /* No flag restriction */
+
 enum stat_item {
 	ALLOC_FASTPATH,		/* Allocation from cpu slab */
 	ALLOC_SLOWPATH,		/* Allocation by getting a new cpu slab */
diff --git a/mm/slab.c b/mm/slab.c
index 8524923..8c1d447 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -162,23 +162,6 @@
  */
 static bool pfmemalloc_active __read_mostly;
 
-/* Legal flag mask for kmem_cache_create(). */
-#if DEBUG
-# define CREATE_MASK	(SLAB_RED_ZONE | \
-			 SLAB_POISON | SLAB_HWCACHE_ALIGN | \
-			 SLAB_CACHE_DMA | \
-			 SLAB_STORE_USER | \
-			 SLAB_RECLAIM_ACCOUNT | SLAB_PANIC | \
-			 SLAB_DESTROY_BY_RCU | SLAB_MEM_SPREAD | \
-			 SLAB_DEBUG_OBJECTS | SLAB_NOLEAKTRACE | SLAB_NOTRACK)
-#else
-# define CREATE_MASK	(SLAB_HWCACHE_ALIGN | \
-			 SLAB_CACHE_DMA | \
-			 SLAB_RECLAIM_ACCOUNT | SLAB_PANIC | \
-			 SLAB_DESTROY_BY_RCU | SLAB_MEM_SPREAD | \
-			 SLAB_DEBUG_OBJECTS | SLAB_NOLEAKTRACE | SLAB_NOTRACK)
-#endif
-
 /*
  * kmem_bufctl_t:
  *
@@ -2385,11 +2368,6 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
 	if (flags & SLAB_DESTROY_BY_RCU)
 		BUG_ON(flags & SLAB_POISON);
 #endif
-	/*
-	 * Always checks flags, a caller might be expecting debug support which
-	 * isn't available.
-	 */
-	BUG_ON(flags & ~CREATE_MASK);
 
 	/*
 	 * Check that size is in terms of words.  This is needed to avoid
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 9c21725..79be32e 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -107,6 +107,13 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align
 	if (!kmem_cache_sanity_check(name, size) == 0)
 		goto out_locked;
 
+	/*
+	 * Some allocators will constraint the set of valid flags to a subset
+	 * of all flags. We expect them to define CACHE_CREATE_MASK in this
+	 * case, and we'll just provide them with a sanitized version of the
+	 * passed flags.
+	 */
+	flags &= SLAB_AVAILABLE_FLAGS;
 
 	s = __kmem_cache_alias(name, size, align, flags, ctor);
 	if (s)
-- 
1.7.11.4

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