[PATCH 2/2] dma-debug: Update DMA debug API to better handlemultiple mappings of a buffer

From: Alexander Duyck
Date: Mon Mar 18 2013 - 18:15:11 EST

There were reports of the igb driver unmapping buffers without calling
dma_mapping_error. On closer inspection issues were found in the DMA debug
API and how it handled multiple mappings of the same buffer.

The issue I found is the fact that the debug_dma_mapping_error would only set
the map_err_type to MAP_ERR_CHECKED in the case that the was only one match
for device and device address. However in the case of non-IOMMU, multiple
addresses existed and as a result it was not setting this field once a
second mapping was instantiated. I have resolved this by changing the search
so that it instead will now set MAP_ERR_CHECKED on the first buffer that
matches the device and DMA address that is currently in the state

A secondary side effect of this patch is that in the case of multiple buffers
using the same address only the last mapping will have a valid map_err_type.
The previous mappings will all end up with map_err_type set to
MAP_ERR_CHECKED because of the dma_mapping_error call in debug_dma_map_page.
However this behavior may be preferable as it means you will likely only see
one real error per multi-mapped buffer, versus the current behavior of
multiple false errors mer multi-mapped buffer.

Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxx>
lib/dma-debug.c | 24 +++++++++++++++++++-----
1 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 724bd4d..aa465d9 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -1082,13 +1082,27 @@ void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
ref.dev = dev;
ref.dev_addr = dma_addr;
bucket = get_hash_bucket(&ref, &flags);
- entry = bucket_find_exact(bucket, &ref);

- if (!entry)
- goto out;
+ list_for_each_entry(entry, &bucket->list, list) {
+ if (!exact_match(&ref, entry))
+ continue;
+ /*
+ * The same physical address can be mapped multiple
+ * times. Without a hardware IOMMU this results in the
+ * same device addresses being put into the dma-debug
+ * hash multiple times too. This can result in false
+ * positives being reported. Therefore we implement a
+ * best-fit algorithm here which updates the first entry
+ * from the hash which fits the reference value and is
+ * not currently listed as being checked.
+ */
+ if (entry->map_err_type == MAP_ERR_NOT_CHECKED) {
+ entry->map_err_type = MAP_ERR_CHECKED;
+ break;
+ }
+ }

- entry->map_err_type = MAP_ERR_CHECKED;
put_hash_bucket(bucket, &flags);

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/