dma_pool_create() needs to unlock the mutex in error case.  The bug was
introduced in the 3.16 by commit 
cc6b664aa26d ("mm/dmapool.c: remove
redundant NULL check for dev in dma_pool_create()")/
Signed-off-by: Krzysztof Hałasa <khc@piap.pl>
Cc: stable@vger.kernel.org  # v3.16
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
        if (list_empty(&dev->dma_pools) &&
            device_create_file(dev, &dev_attr_pools)) {
                kfree(retval);
-               return NULL;
+               retval = NULL;
        } else
                list_add(&retval->pools, &dev->dma_pools);
        mutex_unlock(&pools_lock);