dmaengine: fix broken device refcounting

When a DMA device is unregistered, its reference count is decremented twice
for each channel: Once dma_class_dev_release() and once in
dma_chan_cleanup().  This may result in the DMA device driver's remove()
function completing before all channels have been cleaned up, causing lots
of use-after-free fun.

Fix it by incrementing the device's reference count twice for each
channel during registration.

[dan.j.williams@intel.com: kill unnecessary client refcounting]
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 8248992..d59b2f4 100644 (file)
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -182,10 +182,9 @@ static void dma_client_chan_alloc(struct dma_client *client)
                                /* we are done once this client rejects
                                 * an available resource
                                 */
-                               if (ack == DMA_ACK) {
+                               if (ack == DMA_ACK)
                                        dma_chan_get(chan);
-                                       kref_get(&device->refcount);
-                               } else if (ack == DMA_NAK)
+                               else if (ack == DMA_NAK)
                                        return;
                        }
                }
@@ -272,11 +271,8 @@ static void dma_clients_notify_removed(struct dma_chan *chan)
                /* client was holding resources for this channel so
                 * free it
                 */
-               if (ack == DMA_ACK) {
+               if (ack == DMA_ACK)
                        dma_chan_put(chan);
-                       kref_put(&chan->device->refcount,
-                               dma_async_device_cleanup);
-               }
        }
 
        mutex_unlock(&dma_list_mutex);
@@ -316,11 +312,8 @@ void dma_async_client_unregister(struct dma_client *client)
                        ack = client->event_callback(client, chan,
                                DMA_RESOURCE_REMOVED);
 
-                       if (ack == DMA_ACK) {
+                       if (ack == DMA_ACK)
                                dma_chan_put(chan);
-                               kref_put(&chan->device->refcount,
-                                       dma_async_device_cleanup);
-                       }
                }
 
        list_del(&client->global_node);
@@ -397,6 +390,8 @@ int dma_async_device_register(struct dma_device *device)
                        goto err_out;
                }
 
+               /* One for the channel, one of the class device */
+               kref_get(&device->refcount);
                kref_get(&device->refcount);
                kref_init(&chan->refcount);
                chan->slow_ref = 0;