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

From: Shaun Ruffell
Date: Thu Dec 17 2009 - 19:45:58 EST

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_entry_hash array is always
initialized to a valid state.

Signed-off-by: Shaun Ruffell <sruffell@xxxxxxxxxx>
lib/dma-debug.c | 9 ++++++---
1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index d9b08e0..a504ead 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -697,6 +697,9 @@ 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");
@@ -715,14 +718,14 @@ void dma_debug_init(u32 num_entries)
int i;

- if (global_disable)
- return;
for (i = 0; i < HASH_SIZE; ++i) {

+ if (global_disable)
+ return;
if (dma_debug_fs_init() != 0) {
pr_err("DMA-API: error creating debugfs entries - disabling\n");
global_disable = true;

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