[PATCH 1/2] dma-debug: Do not add notifier when dma debugging is disabled.

From: Joerg Roedel
Date: Mon Dec 21 2009 - 10:22:45 EST

From: Shaun Ruffell <sruffell@xxxxxxxxxx>

If CONFIG_HAVE_DMA_API_DEBUG is defined and "dma_debug=off" is
specified on the kernel command line, when you detach a driver from a
device you can cause the following NULL pointer dereference:

BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<c0580d35>] dma_debug_device_change+0x5d/0x117

The problem is that the dma_debug_device_change notifier function is
added to the bus notifier chain even though the dma_entry_hash array
was never initialized. If dma debugging is disabled, this patch both
prevents dma_debug_device_change notifiers from being added to the
chain, and additionally ensures that the dma_debug_device_change
notifier function is a no-op.

Cc: stable@xxxxxxxxxx
Signed-off-by: Shaun Ruffell <sruffell@xxxxxxxxxx>
Signed-off-by: Joerg Roedel <joerg.roedel@xxxxxxx>
lib/dma-debug.c | 5 +++++
1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index d9b08e0..7399744 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -676,6 +676,8 @@ static int dma_debug_device_change(struct notifier_block *nb,
struct device *dev = data;
int count;

+ if (global_disable)
+ return;

switch (action) {
@@ -697,6 +699,9 @@ void dma_debug_add_bus(struct bus_type *bus)
struct notifier_block *nb;

+ if (global_disable)
+ return;
nb = kzalloc(sizeof(struct notifier_block), GFP_KERNEL);
if (nb == NULL) {
pr_err("dma_debug_add_bus: out of memory\n");

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/