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 <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/slub.c b/mm/slub.c
index 2b50b97a0fc3fd8bac4bf3e601c52a53e004a6bf..f93adb915c00bedf53e114eb7fda163ef84a590e 100644 (file)
--- 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