slab allocators: Remove SLAB_DEBUG_INITIAL flag

I have never seen a use of SLAB_DEBUG_INITIAL.  It is only supported by
SLAB.

I think its purpose was to have a callback after an object has been freed
to verify that the state is the constructor state again?  The callback is
performed before each freeing of an object.

I would think that it is much easier to check the object state manually
before the free.  That also places the check near the code object
manipulation of the object.

Also the SLAB_DEBUG_INITIAL callback is only performed if the kernel was
compiled with SLAB debugging on.  If there would be code in a constructor
handling SLAB_DEBUG_INITIAL then it would have to be conditional on
SLAB_DEBUG otherwise it would just be dead code.  But there is no such code
in the kernel.  I think SLUB_DEBUG_INITIAL is too problematic to make real
use of, difficult to understand and there are easier ways to accomplish the
same effect (i.e.  add debug code before kfree).

There is a related flag SLAB_CTOR_VERIFY that is frequently checked to be
clear in fs inode caches.  Remove the pointless checks (they would even be
pointless without removeal of SLAB_DEBUG_INITIAL) from the fs constructors.

This is the last slab flag that SLUB did not support.  Remove the check for
unimplemented flags from SLUB.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 18 deletions

diff --git a/mm/slab.c b/mm/slab.c
index 2a3cbd6e675d..a877d6f3d687 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -116,8 +116,7 @@
 #include        <asm/page.h>
 
 /*
- * DEBUG        - 1 for kmem_cache_create() to honour; SLAB_DEBUG_INITIAL,
- *                SLAB_RED_ZONE & SLAB_POISON.
+ * DEBUG        - 1 for kmem_cache_create() to honour; SLAB_RED_ZONE & SLAB_POISON.
  *                0 for faster, smaller code (especially in the critical paths).
  *
  * STATS        - 1 to collect stats for /proc/slabinfo.
@@ -172,7 +171,7 @@
 
 /* Legal flag mask for kmem_cache_create(). */
 #if DEBUG
-# define CREATE_MASK    (SLAB_DEBUG_INITIAL | SLAB_RED_ZONE | \
+# define CREATE_MASK    (SLAB_RED_ZONE | \
                          SLAB_POISON | SLAB_HWCACHE_ALIGN | \
                          SLAB_CACHE_DMA | \
                          SLAB_STORE_USER | \
@@ -2184,12 +2183,6 @@ kmem_cache_create (const char *name, size_t size, size_t align,
 
 #if DEBUG
         WARN_ON(strchr(name, ' '));     /* It confuses parsers */
-        if ((flags & SLAB_DEBUG_INITIAL) && !ctor) {
-                /* No constructor, but inital state check requested */
-                printk(KERN_ERR "%s: No con, but init state check "
-                       "requested - %s\n", __FUNCTION__, name);
-                flags &= ~SLAB_DEBUG_INITIAL;
-        }
 #if FORCED_DEBUG
         /*
          * Enable redzoning and last user accounting, except for caches with
@@ -2895,15 +2888,6 @@ static void *cache_free_debugcheck(struct kmem_cache *cachep, void *objp,
         BUG_ON(objnr >= cachep->num);
         BUG_ON(objp != index_to_obj(cachep, slabp, objnr));
 
-        if (cachep->flags & SLAB_DEBUG_INITIAL) {
-                /*
-                 * Need to call the slab's constructor so the caller can
-                 * perform a verify of its state (debugging).  Called without
-                 * the cache-lock held.
-                 */
-                cachep->ctor(objp + obj_offset(cachep),
-                             cachep, SLAB_CTOR_CONSTRUCTOR | SLAB_CTOR_VERIFY);
-        }
         if (cachep->flags & SLAB_POISON && cachep->dtor) {
                 /* we want to cache poison the object,
                  * call the destruction callback