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>

1 files changed, 6 insertions, 11 deletions

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 82489923af09..d59b2f417306 100644
--- 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;