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

From: Shuah Khan
Date: Thu Oct 04 2012 - 18:19:16 EST

On Thu, 2012-10-04 at 13:38 -0400, Konrad Rzeszutek Wilk wrote:
> 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.
I tabbed the existing fields over for readability. Guess I should have
avoided the churn and left it alone. Will fix the tabs and send v4.

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

Is it ok to add your reviewed by tag when I send v4?

-- Shuah
>
> > #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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