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Subject[PATCH] dma-debug: Add dma map/unmap error tracking support
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A recent dma mapping error analysis effort showed that a large precentage
of dma_map_single() and dma_map_page() returns are not checked for mapping
errors. Reference: https://lkml.org/lkml/2012/8/10/326

Adding support for tracking dma mapping and unmapping errors to help assess
the following:

When do dma mapping errors get detected?
How often do these errors occur?
Why don't we see failures related to missing dma mapping error checks?
Are they silent failures?

Signed-off-by: Shuah Khan <shuah.khan@hp.com>
---
Documentation/DMA-API.txt | 7 +++++++
lib/dma-debug.c | 26 +++++++++++++++++++++++++-
2 files changed, 32 insertions(+), 1 deletion(-)
diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index 66bd97a..ee10a11 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -638,6 +638,13 @@ this directory the following files can currently be found:
dma-api/error_count This file is read-only and shows the total
numbers of errors found.

+ dma-api/dma_map_errors This file is read-only and shows the total
+ number of dma mapping errors detected.
+
+ dma-api/dma_unmap_errors
+ This file is read-only and shows the total
+ number of invalid dma unmapping attempts.
+
dma-api/num_errors The number in this file shows how many
warnings will be printed to the kernel log
before it stops. This number is initialized to
diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 66ce414..8596114 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -83,6 +83,10 @@ static u32 global_disable __read_mostly;
/* Global error count */
static u32 error_count;

+/* dma mapping error counts */
+static u32 dma_map_errors;
+static u32 dma_unmap_errors;
+
/* Global error show enable*/
static u32 show_all_errors __read_mostly;
/* Number of errors to show */
@@ -104,6 +108,8 @@ static struct dentry *show_num_errors_dent __read_mostly;
static struct dentry *num_free_entries_dent __read_mostly;
static struct dentry *min_free_entries_dent __read_mostly;
static struct dentry *filter_dent __read_mostly;
+static struct dentry *dma_map_errors_dent __read_mostly;
+static struct dentry *dma_unmap_errors_dent __read_mostly;

/* per-driver filter related state */

@@ -695,6 +701,19 @@ static int dma_debug_fs_init(void)
if (!filter_dent)
goto out_err;

+ dma_map_errors_dent = debugfs_create_u32("dma_map_errors", 0444,
+ dma_debug_dent,
+ &dma_map_errors);
+
+ if (!dma_map_errors_dent)
+ goto out_err;
+
+ dma_unmap_errors_dent = debugfs_create_u32("dma_unmap_errors", 0444,
+ dma_debug_dent,
+ &dma_unmap_errors);
+ if (!dma_unmap_errors_dent)
+ goto out_err;
+
return 0;

out_err:
@@ -850,6 +869,7 @@ static void check_unmap(struct dma_debug_entry *ref)
unsigned long flags;

if (dma_mapping_error(ref->dev, ref->dev_addr)) {
+ dma_unmap_errors += 1;
err_printk(ref->dev, NULL, "DMA-API: device driver tries "
"to free an invalid DMA memory address\n");
return;
@@ -1022,8 +1042,12 @@ void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,
if (unlikely(global_disable))
return;

- if (unlikely(dma_mapping_error(dev, dma_addr)))
+ if (unlikely(dma_mapping_error(dev, dma_addr))) {
+ dma_map_errors += 1;
+ err_printk(dev, NULL,
+ "DMA-API: dma_map_page() returned error\n");
return;
+ }

entry = dma_entry_alloc();
if (!entry)
--
1.7.9.5




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