--- /dev/null
+/*
+ * Regression2
+ * Description:
+ * Toshiyuki Okajima describes the following radix-tree bug:
+ *
+ * In the following case, we can get a hangup on
+ * radix_radix_tree_gang_lookup_tag_slot.
+ *
+ * 0. The radix tree contains RADIX_TREE_MAP_SIZE items. And the tag of
+ * a certain item has PAGECACHE_TAG_DIRTY.
+ * 1. radix_tree_range_tag_if_tagged(, start, end, , PAGECACHE_TAG_DIRTY,
+ * PAGECACHE_TAG_TOWRITE) is called to add PAGECACHE_TAG_TOWRITE tag
+ * for the tag which has PAGECACHE_TAG_DIRTY. However, there is no tag with
+ * PAGECACHE_TAG_DIRTY within the range from start to end. As the result,
+ * There is no tag with PAGECACHE_TAG_TOWRITE but the root tag has
+ * PAGECACHE_TAG_TOWRITE.
+ * 2. An item is added into the radix tree and then the level of it is
+ * extended into 2 from 1. At that time, the new radix tree node succeeds
+ * the tag status of the root tag. Therefore the tag of the new radix tree
+ * node has PAGECACHE_TAG_TOWRITE but there is not slot with
+ * PAGECACHE_TAG_TOWRITE tag in the child node of the new radix tree node.
+ * 3. The tag of a certain item is cleared with PAGECACHE_TAG_DIRTY.
+ * 4. All items within the index range from 0 to RADIX_TREE_MAP_SIZE - 1 are
+ * released. (Only the item which index is RADIX_TREE_MAP_SIZE exist in the
+ * radix tree.) As the result, the slot of the radix tree node is NULL but
+ * the tag which corresponds to the slot has PAGECACHE_TAG_TOWRITE.
+ * 5. radix_tree_gang_lookup_tag_slot(PAGECACHE_TAG_TOWRITE) calls
+ * __lookup_tag. __lookup_tag returns with 0. And __lookup_tag doesn't
+ * change the index that is the input and output parameter. Because the 1st
+ * slot of the radix tree node is NULL, but the tag which corresponds to
+ * the slot has PAGECACHE_TAG_TOWRITE.
+ * Therefore radix_tree_gang_lookup_tag_slot tries to get some items by
+ * calling __lookup_tag, but it cannot get any items forever.
+ *
+ * The fix is to change that radix_tree_tag_if_tagged doesn't tag the root tag
+ * if it doesn't set any tags within the specified range.
+ *
+ * Running:
+ * This test should run to completion immediately. The above bug would cause it
+ * to hang indefinitely.
+ *
+ * Upstream commit:
+ * Not yet
+ */
+#include <linux/kernel.h>
+#include <linux/gfp.h>
+#include <linux/slab.h>
+#include <linux/radix-tree.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "regression.h"
+
+#ifdef __KERNEL__
+#define RADIX_TREE_MAP_SHIFT (CONFIG_BASE_SMALL ? 4 : 6)
+#else
+#define RADIX_TREE_MAP_SHIFT 3 /* For more stressful testing */
+#endif
+
+#define RADIX_TREE_MAP_SIZE (1UL << RADIX_TREE_MAP_SHIFT)
+#define PAGECACHE_TAG_DIRTY 0
+#define PAGECACHE_TAG_WRITEBACK 1
+#define PAGECACHE_TAG_TOWRITE 2
+
+static RADIX_TREE(mt_tree, GFP_KERNEL);
+unsigned long page_count = 0;
+
+struct page {
+ unsigned long index;
+};
+
+static struct page *page_alloc(void)
+{
+ struct page *p;
+ p = malloc(sizeof(struct page));
+ p->index = page_count++;
+
+ return p;
+}
+
+void regression2_test(void)
+{
+ int i;
+ struct page *p;
+ int max_slots = RADIX_TREE_MAP_SIZE;
+ unsigned long int start, end;
+ struct page *pages[1];
+
+ printf("running regression test 2 (should take milliseconds)\n");
+ /* 0. */
+ for (i = 0; i <= max_slots - 1; i++) {
+ p = page_alloc();
+ radix_tree_insert(&mt_tree, i, p);
+ }
+ radix_tree_tag_set(&mt_tree, max_slots - 1, PAGECACHE_TAG_DIRTY);
+
+ /* 1. */
+ start = 0;
+ end = max_slots - 2;
+ radix_tree_range_tag_if_tagged(&mt_tree, &start, end, 1,
+ PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
+
+ /* 2. */
+ p = page_alloc();
+ radix_tree_insert(&mt_tree, max_slots, p);
+
+ /* 3. */
+ radix_tree_tag_clear(&mt_tree, max_slots - 1, PAGECACHE_TAG_DIRTY);
+
+ /* 4. */
+ for (i = max_slots - 1; i >= 0; i--)
+ radix_tree_delete(&mt_tree, i);
+
+ /* 5. */
+ // NOTE: start should not be 0 because radix_tree_gang_lookup_tag_slot
+ // can return.
+ start = 1;
+ end = max_slots - 2;
+ radix_tree_gang_lookup_tag_slot(&mt_tree, (void ***)pages, start, end,
+ PAGECACHE_TAG_TOWRITE);
+
+ /* We remove all the remained nodes */
+ radix_tree_delete(&mt_tree, max_slots);
+
+ printf("regression test 2, done\n");
+}
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