SLUB: do proper locking during dma slab creation

We modify the kmalloc_cache_dma[] array without proper locking.  Do the proper
locking and undo the dma cache creation if another processor has already
created it.

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, 9 insertions, 2 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 2b50b97a0fc3..f93adb915c00 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2301,8 +2301,15 @@ static noinline struct kmem_cache *dma_kmalloc_cache(int index, gfp_t flags)
         text = kasprintf(flags & ~SLUB_DMA, "kmalloc_dma-%d",
                         (unsigned int)realsize);
         s = create_kmalloc_cache(x, text, realsize, flags);
-        kmalloc_caches_dma[index] = s;
-        return s;
+        down_write(&slub_lock);
+        if (!kmalloc_caches_dma[index]) {
+                kmalloc_caches_dma[index] = s;
+                up_write(&slub_lock);
+                return s;
+        }
+        up_write(&slub_lock);
+        kmem_cache_destroy(s);
+        return kmalloc_caches_dma[index];
 }
 #endif