Re: [PATCH v3] dma-debug: New interfaces to debug dma mapping errors

[Konrad Rzeszutek Wilk]

On Wed, Oct 03, 2012 at 08:55:59AM -0600, Shuah Khan wrote:
> A recent dma mapping error analysis effort showed that a large percentage
> of dma_map_single() and dma_map_page() returns are not checked for mapping
> errors.
> 
> Reference:
> http://linuxdriverproject.org/mediawiki/index.php/DMA_Mapping_Error_Analysis
> 
> 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?
> 
> Patch v3: Addresses review and design comments from Patch v2.
> Patch v2: Addressed design issues from Patch v1.
> 
> Enhance dma-debug infrastructure to track dma mapping, and unmapping errors.
> 
> map_errors: (system wide counter)
>   Total number of dma mapping errors returned by the dma mapping interfaces,
>   in response to mapping requests from all devices in the system.
> map_errors_not_checked: (system wide counter)
>   Total number of dma mapping errors devices failed to check before using
>   the returned address.
> unmap_errors: (system wide counter)
>   Total number of times devices tried to unmap or free an invalid dma
>   address.
> map_err_type: (new field added to dma_debug_entry structure)
>   New field to maintain dma mapping error check status. This error type
>   is applicable to the dma map page and dma map single entries tracked by
>   dma-debug api. This status indicates whether or not a good mapping is
>   checked by the device before its use. dma_map_single() and dma_map_page()
>   could fail to create a mapping in some cases, and drivers are expected to
>   call dma_mapping_error() to check for errors. Please note that this is not
>   counter.
> 
> Enhancements to dma-debug api are made to add new debugfs interfaces to
> report total dma errors, dma errors that are not checked, and unmap errors
> for the entire system. Please note that these are system wide counters for
> all devices in the system.
> 
> The following new dma-debug interface is added:
> 
> debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
> 	Sets dma map error checked status for the dma map entry if one is
> 	found. Decrements the system wide dma_map_errors_not_checked counter
> 	that is incremented by debug_dma_map_page() when it checks for
> 	mapping error before adding it to the dma debug entry table.
> 
> New dma-debug internal interface:
> check_mapping_error(struct device *dev, dma_addr_t dma_addr)
> Calling dma_mapping_error() from dma-debug api will result in dma mapping
> check when it shouldn't. This internal routine checks dma mapping error
> without any debug checks. 
> 
> The following existing dma-debug api are changed to support this feature:
> debug_dma_map_page()
> 	Increments dma_map_errors and dma_map_errors_not_checked errors totals
> 	for the system, dma-debug api keeps track of, when dma_addr is invalid.
> 	This routine now calls internal check_mapping_error() interface to
> 	avoid doing dma mapping debug checks from dma-debug internal mapping
> 	error checks.
> check_unmap()
> 	This is an existing internal routines that checks for various mapping
> 	errors. Changed to increment system wide dma_unmap_errors, when a
> 	device requests an invalid address to be unmapped. This routine now
> 	calls internal check_mapping_error() interface to avoid doing dma
> 	mapping debug checks from dma-debug internal mapping error checks.
> 
> Changed arch/x86/include/asm/dma-mapping.h to call debug_dma_mapping_error()
> to validate these new interfaces on x86_64. Other architectures will be
> changed in a subsequent patch.
> 
> Tested: Intel iommu and swiotlb (iommu=soft) on x86-64 with
>         CONFIG_DMA_API_DEBUG enabled and disabled.
> 
> Signed-off-by: Shuah Khan <shuah.khan@xxxxxx>
> ---
>  Documentation/DMA-API.txt          |   13 ++++
>  arch/x86/include/asm/dma-mapping.h |    1 +
>  include/linux/dma-debug.h          |    7 ++
>  lib/dma-debug.c                    |  128 ++++++++++++++++++++++++++++++++----
>  4 files changed, 136 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
> index 66bd97a..886aaf9 100644
> --- a/Documentation/DMA-API.txt
> +++ b/Documentation/DMA-API.txt
> @@ -638,6 +638,19 @@ 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/map_errors	This file is read-only and shows the total
> +				number of dma mapping errors detected.
> +
> +	dma-api/map_errors_not_checked
> +				This file is read-only and shows the total
> +				number of dma mapping errors, device drivers
> +				failed to check prior to using the returned
> +				address.
> +
> +	dma-api/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/arch/x86/include/asm/dma-mapping.h b/arch/x86/include/asm/dma-mapping.h
> index f7b4c79..808dae6 100644
> --- a/arch/x86/include/asm/dma-mapping.h
> +++ b/arch/x86/include/asm/dma-mapping.h
> @@ -47,6 +47,7 @@ static inline struct dma_map_ops *get_dma_ops(struct device *dev)
>  static inline int dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
>  {
>  	struct dma_map_ops *ops = get_dma_ops(dev);
> +	debug_dma_mapping_error(dev, dma_addr);
>  	if (ops->mapping_error)
>  		return ops->mapping_error(dev, dma_addr);
>  
> diff --git a/include/linux/dma-debug.h b/include/linux/dma-debug.h
> index 171ad8a..fc0e34c 100644
> --- a/include/linux/dma-debug.h
> +++ b/include/linux/dma-debug.h
> @@ -39,6 +39,8 @@ extern void debug_dma_map_page(struct device *dev, struct page *page,
>  			       int direction, dma_addr_t dma_addr,
>  			       bool map_single);
>  
> +extern void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr);
> +
>  extern void debug_dma_unmap_page(struct device *dev, dma_addr_t addr,
>  				 size_t size, int direction, bool map_single);
>  
> @@ -105,6 +107,11 @@ static inline void debug_dma_map_page(struct device *dev, struct page *page,
>  {
>  }
>  
> +static inline void debug_dma_mapping_error(struct device *dev,
> +					  dma_addr_t dma_addr)
> +{
> +}
> +
>  static inline void debug_dma_unmap_page(struct device *dev, dma_addr_t addr,
>  					size_t size, int direction,
>  					bool map_single)
> diff --git a/lib/dma-debug.c b/lib/dma-debug.c
> index 66ce414..1708a10 100644
> --- a/lib/dma-debug.c
> +++ b/lib/dma-debug.c
> @@ -45,18 +45,25 @@ enum {
>  	dma_debug_coherent,
>  };
>  
> +enum map_err_types {
> +	MAP_ERR_CHECK_NOT_APPLICABLE,
> +	MAP_ERR_NOT_CHECKED,
> +	MAP_ERR_CHECKED,
> +};
> +
>  #define DMA_DEBUG_STACKTRACE_ENTRIES 5
>  
>  struct dma_debug_entry {
> -	struct list_head list;
> -	struct device    *dev;
> -	int              type;
> -	phys_addr_t      paddr;
> -	u64              dev_addr;
> -	u64              size;
> -	int              direction;
> -	int		 sg_call_ents;
> -	int		 sg_mapped_ents;
> +	struct list_head    list;
> +	struct device       *dev;
> +	int                 type;
> +	phys_addr_t         paddr;
> +	u64                 dev_addr;
> +	u64                 size;
> +	int                 direction;
> +	int		    sg_call_ents;
> +	int		    sg_mapped_ents;
> +	enum map_err_types  map_err_type;

Something gone wild with your tabs/space. It should be only
one extra field added.

Otherwise:
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

>  #ifdef CONFIG_STACKTRACE
>  	struct		 stack_trace stacktrace;
>  	unsigned long	 st_entries[DMA_DEBUG_STACKTRACE_ENTRIES];
> @@ -83,6 +90,11 @@ static u32 global_disable __read_mostly;
>  /* Global error count */
>  static u32 error_count;
>  
> +/* dma mapping error counts */
> +static u32 map_errors;
> +static u32 map_errors_not_checked;
> +static u32 unmap_errors;
> +
>  /* Global error show enable*/
>  static u32 show_all_errors __read_mostly;
>  /* Number of errors to show */
> @@ -104,6 +116,9 @@ 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 *map_errors_dent   __read_mostly;
> +static struct dentry *map_errors_not_checked_dent   __read_mostly;
> +static struct dentry *unmap_errors_dent __read_mostly;
>  
>  /* per-driver filter related state */
>  
> @@ -114,6 +129,12 @@ static struct device_driver *current_driver                    __read_mostly;
>  
>  static DEFINE_RWLOCK(driver_name_lock);
>  
> +static const char *const maperr2str[] = {
> +	[MAP_ERR_CHECK_NOT_APPLICABLE] = "dma map error check not applicable",
> +	[MAP_ERR_NOT_CHECKED] = "dma map error not checked",
> +	[MAP_ERR_CHECKED] = "dma map error checked",
> +};
> +
>  static const char *type2name[4] = { "single", "page",
>  				    "scather-gather", "coherent" };
>  
> @@ -381,11 +402,12 @@ void debug_dma_dump_mappings(struct device *dev)
>  		list_for_each_entry(entry, &bucket->list, list) {
>  			if (!dev || dev == entry->dev) {
>  				dev_info(entry->dev,
> -					 "%s idx %d P=%Lx D=%Lx L=%Lx %s\n",
> +					 "%s idx %d P=%Lx D=%Lx L=%Lx %s %s\n",
>  					 type2name[entry->type], idx,
>  					 (unsigned long long)entry->paddr,
>  					 entry->dev_addr, entry->size,
> -					 dir2name[entry->direction]);
> +					 dir2name[entry->direction],
> +					 maperr2str[entry->map_err_type]);
>  			}
>  		}
>  
> @@ -695,6 +717,28 @@ static int dma_debug_fs_init(void)
>  	if (!filter_dent)
>  		goto out_err;
>  
> +	map_errors_dent = debugfs_create_u32("map_errors", 0444,
> +			dma_debug_dent,
> +			&map_errors);
> +
> +	if (!map_errors_dent)
> +		goto out_err;
> +
> +	map_errors_not_checked_dent = debugfs_create_u32(
> +			"map_errors_not_checked",
> +			0444,
> +			dma_debug_dent,
> +			&map_errors_not_checked);
> +
> +	if (!map_errors_not_checked_dent)
> +		goto out_err;
> +
> +	unmap_errors_dent = debugfs_create_u32("unmap_errors", 0444,
> +			dma_debug_dent,
> +			&unmap_errors);
> +	if (!unmap_errors_dent)
> +		goto out_err;
> +
>  	return 0;
>  
>  out_err:
> @@ -843,13 +887,29 @@ static __init int dma_debug_entries_cmdline(char *str)
>  __setup("dma_debug=", dma_debug_cmdline);
>  __setup("dma_debug_entries=", dma_debug_entries_cmdline);
>  
> +/* Calling dma_mapping_error() from dma-debug api will result in calling
> +   debug_dma_mapping_error() - need internal mapping error routine to
> +   avoid debug checks */
> +#ifndef DMA_ERROR_CODE
> +#define DMA_ERROR_CODE 0
> +#endif
> +static inline int check_mapping_error(struct device *dev, dma_addr_t dma_addr)
> +{
> +	const struct dma_map_ops *ops = get_dma_ops(dev);
> +	if (ops->mapping_error)
> +		return ops->mapping_error(dev, dma_addr);
> +
> +	return (dma_addr == DMA_ERROR_CODE);
> +}
> +
>  static void check_unmap(struct dma_debug_entry *ref)
>  {
>  	struct dma_debug_entry *entry;
>  	struct hash_bucket *bucket;
>  	unsigned long flags;
>  
> -	if (dma_mapping_error(ref->dev, ref->dev_addr)) {
> +	if (unlikely(check_mapping_error(ref->dev, ref->dev_addr))) {
> +		unmap_errors += 1;
>  		err_printk(ref->dev, NULL, "DMA-API: device driver tries "
>  			   "to free an invalid DMA memory address\n");
>  		return;
> @@ -915,6 +975,15 @@ static void check_unmap(struct dma_debug_entry *ref)
>  			   dir2name[ref->direction]);
>  	}
>  
> +	if (entry->map_err_type == MAP_ERR_NOT_CHECKED) {
> +		err_printk(ref->dev, entry,
> +			   "DMA-API: device driver failed to check map error"
> +			   "[device address=0x%016llx] [size=%llu bytes] "
> +			   "[mapped as %s]",
> +			   ref->dev_addr, ref->size,
> +			   type2name[entry->type]);
> +	}
> +
>  	hash_bucket_del(entry);
>  	dma_entry_free(entry);
>  
> @@ -1022,8 +1091,11 @@ 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(check_mapping_error(dev, dma_addr))) {
> +		map_errors += 1;
> +		map_errors_not_checked += 1;
>  		return;
> +	}
>  
>  	entry = dma_entry_alloc();
>  	if (!entry)
> @@ -1035,6 +1107,7 @@ void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,
>  	entry->dev_addr  = dma_addr;
>  	entry->size      = size;
>  	entry->direction = direction;
> +	entry->map_err_type = MAP_ERR_NOT_CHECKED;
>  
>  	if (map_single)
>  		entry->type = dma_debug_single;
> @@ -1050,6 +1123,35 @@ void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,
>  }
>  EXPORT_SYMBOL(debug_dma_map_page);
>  
> +void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
> +{
> +	struct dma_debug_entry ref;
> +	struct dma_debug_entry *entry;
> +	struct hash_bucket *bucket;
> +	unsigned long flags;
> +
> +	if (unlikely(global_disable))
> +		return;
> +
> +	ref.dev = dev;
> +	ref.dev_addr = dma_addr;
> +	bucket = get_hash_bucket(&ref, &flags);
> +	entry = bucket_find_exact(bucket, &ref);
> +
> +	if (!entry) {
> +		/* very likley dma-api didn't call debug_dma_map_page() or
> +		   debug_dma_map_page() detected mapping error */
> +		if (map_errors_not_checked)
> +			map_errors_not_checked -= 1;
> +		goto out;
> +	}
> +
> +	entry->map_err_type = MAP_ERR_CHECKED;
> +out:
> +	put_hash_bucket(bucket, &flags);
> +}
> +EXPORT_SYMBOL(debug_dma_mapping_error);
> +
>  void debug_dma_unmap_page(struct device *dev, dma_addr_t addr,
>  			  size_t size, int direction, bool map_single)
>  {
> -- 
> 1.7.9.5
> 
> 
> 
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