[PATCH 3.2 120/200] dma: ste_dma40: don't dereference free:d descriptor

[Ben Hutchings]

3.2.56-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Linus Walleij <linus.walleij@xxxxxxxxxx>

commit e9baa9d9d520fb0e24cca671e430689de2d4a4b2 upstream.

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.

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Signed-off-by: Vinod Koul <vinod.koul@xxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/dma/ste_dma40.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/dma/ste_dma40.c
+++ b/drivers/dma/ste_dma40.c
@@ -1202,6 +1202,7 @@ static void dma_tasklet(unsigned long da
 	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;
 
@@ -1225,6 +1226,7 @@ static void dma_tasklet(unsigned long da
 	}
 
 	/* Callback to client */
+	callback_active = !!(d40d->txd.flags & DMA_PREP_INTERRUPT);
 	callback = d40d->txd.callback;
 	callback_param = d40d->txd.callback_param;
 
@@ -1249,7 +1251,7 @@ static void dma_tasklet(unsigned long da
 
 	spin_unlock_irqrestore(&d40c->lock, flags);
 
-	if (callback && (d40d->txd.flags & DMA_PREP_INTERRUPT))
+	if (callback_active && callback)
 		callback(callback_param);
 
 	return;

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