On Thu, 09 Jan 2014 12:17:26 -0800 Dan Williams <[email protected]>
wrote:
> Record actively mapped pages and provide an api for asserting a given
> page is dma inactive before execution proceeds. Placing
> debug_dma_assert_idle() in cow_user_page() flagged the violation of the
> dma-api in the NET_DMA implementation (see commit 77873803363c "net_dma:
> mark broken").
>
> --- a/include/linux/dma-debug.h
> +++ b/include/linux/dma-debug.h
> @@ -185,4 +185,10 @@ static inline void debug_dma_dump_mappings(struct device
> *dev)
>
> #endif /* CONFIG_DMA_API_DEBUG */
>
> +#ifdef CONFIG_DMA_VS_CPU_DEBUG
> +extern void debug_dma_assert_idle(struct page *page);
> +#else
> +static inline void debug_dma_assert_idle(struct page *page) { }
Surely this breaks the build when CONFIG_DMA_VS_CPU_DEBUG=n?
lib/dma-debug.c is missing the necessary "#ifdef
CONFIG_DMA_VS_CPU_DEBUG"s.
Do we really need this config setting anyway? What goes bad if we
permanently enable this subfeature when dma debugging is enabled?
>
> ...
>
> index d87a17a819d0..f67ae111cd2f 100644
> --- a/lib/dma-debug.c
> +++ b/lib/dma-debug.c
> @@ -57,7 +57,8 @@ struct dma_debug_entry {
> struct list_head list;
> struct device *dev;
> int type;
> - phys_addr_t paddr;
> + unsigned long pfn;
> + size_t offset;
Some documentation for the fields would be nice. offset of what
relative to what, in what units?
> u64 dev_addr;
> u64 size;
> int direction;
> @@ -372,6 +373,11 @@ static void hash_bucket_del(struct dma_debug_entry
> *entry)
> list_del(&entry->list);
> }
>
>
> ...
>
>
> +/* memory usage is constrained by the maximum number of available
> + * dma-debug entries
> + */
A brief design overview would be useful. What goes in tree, how is it
indexed, when and why do we add/remove/test items, etc.
> +static RADIX_TREE(dma_active_pfn, GFP_NOWAIT);
> +static DEFINE_SPINLOCK(radix_lock);
> +
> +static void __active_pfn_inc_overlap(struct dma_debug_entry *entry)
> +{
> + unsigned long pfn = entry->pfn;
> + int i;
> +
> + for (i = 0; i < RADIX_TREE_MAX_TAGS; i++)
> + if (radix_tree_tag_get(&dma_active_pfn, pfn, i) == 0) {
> + radix_tree_tag_set(&dma_active_pfn, pfn, i);
> + return;
> + }
> + pr_debug("DMA-API: max overlap count (%d) reached for pfn 0x%lx\n",
> + RADIX_TREE_MAX_TAGS, pfn);
> +}
> +
>
> ...
>
> +void debug_dma_assert_idle(struct page *page)
> +{
> + unsigned long flags;
> + struct dma_debug_entry *entry;
> +
> + if (!page)
> + return;
> +
> + spin_lock_irqsave(&radix_lock, flags);
> + entry = radix_tree_lookup(&dma_active_pfn, page_to_pfn(page));
> + spin_unlock_irqrestore(&radix_lock, flags);
> +
> + if (!entry)
> + return;
> +
> + err_printk(entry->dev, entry,
> + "DMA-API: cpu touching an active dma mapped page "
> + "[pfn=0x%lx]\n", entry->pfn);
> +}
> +EXPORT_SYMBOL_GPL(debug_dma_assert_idle);
The export isn't needed for mm/memory.c
>
> ...
>
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