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From: Greg Kroah-Hartman on 4 Jan 2010 19:50
From: Shaun Ruffell <sruffell(a)digium.com>

commit f797d9881b62c2ddb1d2e7bd80d87141949c84aa upstream.

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.

Signed-off-by: Shaun Ruffell <sruffell(a)digium.com>
Signed-off-by: Joerg Roedel <joerg.roedel(a)amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>
---
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 ce6b7ea..dcd43e3 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) {
case BUS_NOTIFY_UNBOUND_DRIVER:
@@ -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");
--
1.6.6

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Prev: ext4: Fix potential quota deadlock
Next: [RFC][PATCH v5] readahead: introduce O_RANDOM for POSIX_FADV_RANDOM