fs, jfs: remove slab object constructor

Mempools based on slab caches with object constructors are risky because
element allocation can happen either from the slab cache itself, meaning
the constructor is properly called before returning, or from the mempool
reserve pool, meaning the constructor is not called before returning,
depending on the allocation context.

For this reason, we should disallow creating mempools based on slab caches
that have object constructors.  Callers of mempool_alloc() will be
responsible for properly initializing the returned element.

Then, it doesn't matter if the element came from the slab cache or the
mempool reserved pool.

The only occurrence of a mempool being based on a slab cache with an
object constructor in the tree is in fs/jfs/jfs_metapage.c.  Remove it and
properly initialize the element in alloc_metapage().

At the same time, META_free is never used, so remove it as well.

Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sebastian Ott <sebott@linux.vnet.ibm.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/jfs/jfs_metapage.c

@@ -183,30 +183,23 @@ static inline void remove_metapage(struct page *page, struct metapage *mp)
 
 #endif
 
-static void init_once(void *foo)
+static inline struct metapage *alloc_metapage(gfp_t gfp_mask)
 {
-	struct metapage *mp = (struct metapage *)foo;
+	struct metapage *mp = mempool_alloc(metapage_mempool, gfp_mask);
 
+	if (mp) {
 		mp->lid = 0;
 		mp->lsn = 0;
-	mp->flag = 0;
 		mp->data = NULL;
 		mp->clsn = 0;
 		mp->log = NULL;
-	set_bit(META_free, &mp->flag);
 		init_waitqueue_head(&mp->wait);
 	}
-
-static inline struct metapage *alloc_metapage(gfp_t gfp_mask)
-{
-	return mempool_alloc(metapage_mempool, gfp_mask);
+	return mp;
 }
 
 static inline void free_metapage(struct metapage *mp)
 {
-	mp->flag = 0;
-	set_bit(META_free, &mp->flag);
-
 	mempool_free(mp, metapage_mempool);
 }
 
@@ -216,7 +209,7 @@ int __init metapage_init(void)
 	 * Allocate the metapage structures
 	 */
 	metapage_cache = kmem_cache_create("jfs_mp", sizeof(struct metapage),
-					   0, 0, init_once);
+					   0, 0, NULL);
 	if (metapage_cache == NULL)
 		return -ENOMEM;
 

fs/jfs/jfs_metapage.h

@@ -48,7 +48,6 @@ struct metapage {
 
 /* metapage flag */
 #define META_locked	0
-#define META_free	1
 #define META_dirty	2
 #define META_sync	3
 #define META_discard	4