[3.11.y.z extended stable] Patch "dma: ste_dma40: don't dereference free:d descriptor" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From f5b4495dc1b99dc0dccae302be8049336aec7c98 Mon Sep 17 00:00:00 2001
From: Linus Walleij <linus.walleij at linaro.org>
Date: Thu, 13 Feb 2014 10:39:01 +0100
Subject: dma: ste_dma40: don't dereference free:d descriptor

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 at oracle.com>
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
Signed-off-by: Vinod Koul <vinod.koul at intel.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/dma/ste_dma40.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c
index 5ab5880..637f4c5 100644
--- a/drivers/dma/ste_dma40.c
+++ b/drivers/dma/ste_dma40.c
@@ -1640,6 +1640,7 @@ 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;

@@ -1667,6 +1668,7 @@ 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;

@@ -1689,7 +1691,7 @@ 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;
--
1.9.0