linux-kernel - [PATCH 31/97] dma-debug: Do not add notifier when dma debugging is disabled.

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Date:	Mon,  4 Jan 2010 16:32:44 -0800
From:	Greg Kroah-Hartman <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org,
	stable-review@...nel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Shaun Ruffell <sruffell@...ium.com>,
	Joerg Roedel <joerg.roedel@....com>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [PATCH 31/97] dma-debug: Do not add notifier when dma debugging is disabled.

From: Shaun Ruffell <sruffell@...ium.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@...ium.com>
Signed-off-by: Joerg Roedel <joerg.roedel@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.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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