Re: [PATCH v2] dma-debug: enhance dma_debug_device_change() to checkfor mapping errors

From: Shuah Khan
Date: Fri Jan 03 2014 - 13:26:20 EST

On 12/30/2013 07:15 AM, Joerg Roedel wrote:
On Wed, Nov 13, 2013 at 01:56:08PM -0700, Shuah Khan wrote:
dma-debug checks to verify if driver validated the address returned by
dma mapping routines when driver does unmap. If a driver doesn't call
unmap, failure to check mapping errors isn't detected and reported.

Enhancing existing bus notifier_call dma_debug_device_change() to check
for mapping errors at the same time it detects leaked dma buffers for
BUS_NOTIFY_UNBOUND_DRIVER event. It scans for mapping errors and if any
found, prints one warning message that includes mapping error count.

Signed-off-by: Shuah Khan <>
lib/dma-debug.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index d87a17a..e34865e 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -717,6 +717,7 @@ static int device_dma_allocations(struct device *dev, struct dma_debug_entry **o
struct dma_debug_entry *entry;
unsigned long flags;
int count = 0, i;
+ int map_err_cnt = 0;


@@ -724,6 +725,8 @@ static int device_dma_allocations(struct device *dev, struct dma_debug_entry **o
list_for_each_entry(entry, &dma_entry_hash[i].list, list) {
if (entry->dev == dev) {
+ if (entry->map_err_type == MAP_ERR_NOT_CHECKED)
+ map_err_cnt += 1;
count += 1;
*out_entry = entry;

I think it is better to check for this in a seperate function and use
err_printk instead of dev_warn in the end to print the errors.
The new function can then be called in the dma_debug_device_change
callback like device_dma_allocations is.

I did explore separate function option and backed off from it since the new routine will have to duplicate what device_dma_allocations() does except that it checks for entry->map_err_type.

I still have the patch that does that saved away. If you still prefer that approach, I can rework the patch and send it.

-- Shuah

Shuah Khan
Senior Linux Kernel Developer - Open Source Group
Samsung Research America(Silicon Valley) | (970) 672-0658
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