dma: ste_dma40: don't dereference free:d descriptor

It appears that in the DMA40 driver the DMA tasklet will very
often dereference memory for a descriptor just free:d from the
DMA40 slab. Nothing happens because no other part of the driver
has yet had a chance to claim this memory, but it's really
nasty to dereference free:d memory, so let's check the flag
before the descriptor is free and store it in a bool variable.

Cc: stable@vger.kernel.org
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c
index 00a2de957b234da060fe5e03592b171f50fa53d1..bf18c786ed40fbaae2a487246df5da85457fbec1 100644 (file)
--- a/drivers/dma/ste_dma40.c
+++ b/drivers/dma/ste_dma40.c
@@ -1641,6 +1641,7 @@ static void dma_tasklet(unsigned long data)
        struct d40_chan *d40c = (struct d40_chan *) data;
        struct d40_desc *d40d;
        unsigned long flags;
+       bool callback_active;
        dma_async_tx_callback callback;
        void *callback_param;
 
@@ -1668,6 +1669,7 @@ static void dma_tasklet(unsigned long data)
        }
 
        /* Callback to client */
+       callback_active = !!(d40d->txd.flags & DMA_PREP_INTERRUPT);
        callback = d40d->txd.callback;
        callback_param = d40d->txd.callback_param;
 
@@ -1690,7 +1692,7 @@ static void dma_tasklet(unsigned long data)
 
        spin_unlock_irqrestore(&d40c->lock, flags);
 
-       if (callback && (d40d->txd.flags & DMA_PREP_INTERRUPT))
+       if (callback_active && callback)
                callback(callback_param);
 
        return;