+ * For each page mapped (initial page in the case of
+ * dma_alloc_coherent/dma_map_{single|page}, or each page in a
+ * scatterlist) insert into this tree using the pfn as the key. At
+ * dma_unmap_{single|sg|page} or dma_free_coherent delete the entry. If
+ * the pfn already exists at insertion time add a tag as a reference
+ * count for the overlapping mappings. For now, the overlap tracking
+ * just ensures that 'unmaps' balance 'maps' before marking the pfn
+ * idle, but we should also be flagging overlaps as an API violation.
+ *
+ * Memory usage is mostly constrained by the maximum number of available
+ * dma-debug entries in that we need a free dma_debug_entry before
+ * inserting into the tree. In the case of dma_map_{single|page} and
+ * dma_alloc_coherent there is only one dma_debug_entry and one pfn to
+ * track per event. dma_map_sg(), on the other hand,
+ * consumes a single dma_debug_entry, but inserts 'nents' entries into
+ * the tree.
+ *
+ * At any time debug_dma_assert_idle() can be called to trigger a
+ * warning if the given page is in the active set.
+ */
+static RADIX_TREE(dma_active_pfn, GFP_NOWAIT);
+static DEFINE_SPINLOCK(radix_lock);
+#define ACTIVE_PFN_MAX_OVERLAP ((1 << RADIX_TREE_MAX_TAGS) - 1)
+
+static int active_pfn_read_overlap(unsigned long pfn)
+{
+ int overlap = 0, i;
+
+ for (i = RADIX_TREE_MAX_TAGS - 1; i >= 0; i--)
+ if (radix_tree_tag_get(&dma_active_pfn, pfn, i))
+ overlap |= 1 << i;
+ return overlap;
+}
+
+static int active_pfn_set_overlap(unsigned long pfn, int overlap)
+{
+ int i;
+
+ if (overlap > ACTIVE_PFN_MAX_OVERLAP || overlap < 0)
+ return 0;
+
+ for (i = RADIX_TREE_MAX_TAGS - 1; i >= 0; i--)
+ if (overlap & 1 << i)
+ radix_tree_tag_set(&dma_active_pfn, pfn, i);
+ else
+ radix_tree_tag_clear(&dma_active_pfn, pfn, i);
+
+ return overlap;
+}
+
+static void active_pfn_inc_overlap(unsigned long pfn)
+{
+ int overlap = active_pfn_read_overlap(pfn);
+
+ overlap = active_pfn_set_overlap(pfn, ++overlap);
+
+ /* If we overflowed the overlap counter then we're potentially
+ * leaking dma-mappings. Otherwise, if maps and unmaps are
+ * balanced then this overflow may cause false negatives in
+ * debug_dma_assert_idle() as the pfn may be marked idle
+ * prematurely.
+ */
+ WARN_ONCE(overlap == 0,
+ "DMA-API: exceeded %d overlapping mappings of pfn %lx\n",
+ ACTIVE_PFN_MAX_OVERLAP, pfn);
+}
+
+static int active_pfn_dec_overlap(unsigned long pfn)
+{
+ int overlap = active_pfn_read_overlap(pfn);
+
+ return active_pfn_set_overlap(pfn, --overlap);
+}
+
+static int active_pfn_insert(struct dma_debug_entry *entry)
+{
+ unsigned long flags;
+ int rc;
+
+ spin_lock_irqsave(&radix_lock, flags);
+ rc = radix_tree_insert(&dma_active_pfn, entry->pfn, entry);
+ if (rc == -EEXIST)
+ active_pfn_inc_overlap(entry->pfn);
+ spin_unlock_irqrestore(&radix_lock, flags);
+
+ return rc;
+}
+
+static void active_pfn_remove(struct dma_debug_entry *entry)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&radix_lock, flags);
+ if (active_pfn_dec_overlap(entry->pfn) == 0)
+ radix_tree_delete(&dma_active_pfn, entry->pfn);
+ spin_unlock_irqrestore(&radix_lock, flags);
+}
+
+/**
+ * debug_dma_assert_idle() - assert that a page is not undergoing dma
+ * @page: page to lookup in the dma_active_pfn tree
+ *
+ * Place a call to this routine in cases where the cpu touching the page
+ * before the dma completes (page is dma_unmapped) will lead to data
+ * corruption.
+ */
+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);
+}
+
+/*