[PATCH v2] mm/slab: simplify SLAB_* flag handling

[Kevin Brodsky]

SLUB is the only remaining allocator. We can therefore get rid of
the logic for allocator-specific flags:

* Merge SLAB_CACHE_FLAGS into SLAB_CORE_FLAGS.

* Remove CACHE_CREATE_MASK and instead mask out SLAB_DEBUG_FLAGS if
  !CONFIG_SLUB_DEBUG. SLAB_DEBUG_FLAGS is now defined
  unconditionally (no impact on existing code, which ignores it if
  !CONFIG_SLUB_DEBUG).

* Define SLAB_FLAGS_PERMITTED in terms of SLAB_CORE_FLAGS and
  SLAB_DEBUG_FLAGS (no functional change).

While at it also remove misleading comments that suggest that
multiple allocators are available.

Signed-off-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
---
v1..v2:
* Keep the SLAB_FLAGS_PERMITTED check and remove CACHE_CREATE_MASK
  instead. SLAB_DEBUG_FLAGS is now defined unconditionally and
  explicitly masked out.

v1: https://lore.kernel.org/all/20250117113226.3484784-1-kevin.brodsky@xxxxxxx/

Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
---
 mm/slab.h        | 32 +++++---------------------------
 mm/slab_common.c | 11 ++---------
 2 files changed, 7 insertions(+), 36 deletions(-)

diff --git a/mm/slab.h b/mm/slab.h
index e9fd9bf0bfa6..1a081f50f947 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -457,39 +457,17 @@ static inline bool is_kmalloc_normal(struct kmem_cache *s)
 	return !(s->flags & (SLAB_CACHE_DMA|SLAB_ACCOUNT|SLAB_RECLAIM_ACCOUNT));
 }
 
-/* Legal flag mask for kmem_cache_create(), for various configurations */
 #define SLAB_CORE_FLAGS (SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA | \
 			 SLAB_CACHE_DMA32 | SLAB_PANIC | \
-			 SLAB_TYPESAFE_BY_RCU | SLAB_DEBUG_OBJECTS )
+			 SLAB_TYPESAFE_BY_RCU | SLAB_DEBUG_OBJECTS | \
+			 SLAB_NOLEAKTRACE | SLAB_RECLAIM_ACCOUNT | \
+			 SLAB_TEMPORARY | SLAB_ACCOUNT | \
+			 SLAB_NO_USER_FLAGS | SLAB_KMALLOC | SLAB_NO_MERGE)
 
-#ifdef CONFIG_SLUB_DEBUG
 #define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
 			  SLAB_TRACE | SLAB_CONSISTENCY_CHECKS)
-#else
-#define SLAB_DEBUG_FLAGS (0)
-#endif
 
-#define SLAB_CACHE_FLAGS (SLAB_NOLEAKTRACE | SLAB_RECLAIM_ACCOUNT | \
-			  SLAB_TEMPORARY | SLAB_ACCOUNT | \
-			  SLAB_NO_USER_FLAGS | SLAB_KMALLOC | SLAB_NO_MERGE)
-
-/* Common flags available with current configuration */
-#define CACHE_CREATE_MASK (SLAB_CORE_FLAGS | SLAB_DEBUG_FLAGS | SLAB_CACHE_FLAGS)
-
-/* Common flags permitted for kmem_cache_create */
-#define SLAB_FLAGS_PERMITTED (SLAB_CORE_FLAGS | \
-			      SLAB_RED_ZONE | \
-			      SLAB_POISON | \
-			      SLAB_STORE_USER | \
-			      SLAB_TRACE | \
-			      SLAB_CONSISTENCY_CHECKS | \
-			      SLAB_NOLEAKTRACE | \
-			      SLAB_RECLAIM_ACCOUNT | \
-			      SLAB_TEMPORARY | \
-			      SLAB_ACCOUNT | \
-			      SLAB_KMALLOC | \
-			      SLAB_NO_MERGE | \
-			      SLAB_NO_USER_FLAGS)
+#define SLAB_FLAGS_PERMITTED (SLAB_CORE_FLAGS | SLAB_DEBUG_FLAGS)
 
 bool __kmem_cache_empty(struct kmem_cache *);
 int __kmem_cache_shutdown(struct kmem_cache *);
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 69f2d19010de..50b9c6497171 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -298,6 +298,8 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
 		static_branch_enable(&slub_debug_enabled);
 	if (flags & SLAB_STORE_USER)
 		stack_depot_init();
+#else
+	flags &= ~SLAB_DEBUG_FLAGS;
 #endif
 
 	mutex_lock(&slab_mutex);
@@ -307,20 +309,11 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
 		goto out_unlock;
 	}
 
-	/* Refuse requests with allocator specific flags */
 	if (flags & ~SLAB_FLAGS_PERMITTED) {
 		err = -EINVAL;
 		goto out_unlock;
 	}
 
-	/*
-	 * 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 &= CACHE_CREATE_MASK;
-
 	/* Fail closed on bad usersize of useroffset values. */
 	if (!IS_ENABLED(CONFIG_HARDENED_USERCOPY) ||
 	    WARN_ON(!args->usersize && args->useroffset) ||

base-commit: ab18b8fff124c9b76ea12692571ca822dcd92854
-- 
2.47.0