Btrfs: extent map selftest: buffered write vs dio read

This test case simulates the racy situation of buffered write vs dio
read, and see if btrfs_get_extent() would return -EEXIST.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/tests/extent-map-tests.c b/fs/btrfs/tests/extent-map-tests.c
index e6f0dd18392eae3a3020a7bd111ffdd790503b39..16830bf88f4662645fb067d2aab002221710fd68 100644 (file)
--- a/fs/btrfs/tests/extent-map-tests.c
+++ b/fs/btrfs/tests/extent-map-tests.c
@@ -182,6 +182,79 @@ out:
        free_extent_map_tree(em_tree);
 }
 
+static void __test_case_3(struct extent_map_tree *em_tree, u64 start)
+{
+       struct extent_map *em;
+       u64 len = SZ_4K;
+       int ret;
+
+       em = alloc_extent_map();
+       if (!em)
+               /* Skip this test on error. */
+               return;
+
+       /* Add [4K, 8K) */
+       em->start = SZ_4K;
+       em->len = SZ_4K;
+       em->block_start = SZ_4K;
+       em->block_len = SZ_4K;
+       ret = add_extent_mapping(em_tree, em, 0);
+       ASSERT(ret == 0);
+       free_extent_map(em);
+
+       em = alloc_extent_map();
+       if (!em)
+               goto out;
+
+       /* Add [0, 16K) */
+       em->start = 0;
+       em->len = SZ_16K;
+       em->block_start = 0;
+       em->block_len = SZ_16K;
+       ret = btrfs_add_extent_mapping(em_tree, &em, start, len);
+       if (ret)
+               test_msg("case3 [0x%llx 0x%llx): ret %d\n",
+                        start, start + len, ret);
+       /*
+        * Since bytes within em are contiguous, em->block_start is identical to
+        * em->start.
+        */
+       if (em &&
+           (start < em->start || start + len > extent_map_end(em) ||
+            em->start != em->block_start || em->len != em->block_len))
+               test_msg(
+"case3 [0x%llx 0x%llx): ret %d em (start 0x%llx len 0x%llx block_start 0x%llx block_len 0x%llx)\n",
+                        start, start + len, ret, em->start, em->len,
+                        em->block_start, em->block_len);
+       free_extent_map(em);
+out:
+       /* free memory */
+       free_extent_map_tree(em_tree);
+}
+
+/*
+ * Test scenario:
+ *
+ * Suppose that no extent map has been loaded into memory yet.
+ * There is a file extent [0, 16K), two jobs are running concurrently
+ * against it, t1 is buffered writing to [4K, 8K) and t2 is doing dio
+ * read from [0, 4K) or [8K, 12K) or [12K, 16K).
+ *
+ * t1 goes ahead of t2 and adds em [4K, 8K) into tree.
+ *
+ *         t1                       t2
+ *  cow_file_range()        btrfs_get_extent()
+ *                            -> lookup_extent_mapping()
+ *   -> add_extent_mapping()
+ *                            -> add_extent_mapping()
+ */
+static void test_case_3(struct extent_map_tree *em_tree)
+{
+       __test_case_3(em_tree, 0);
+       __test_case_3(em_tree, SZ_8K);
+       __test_case_3(em_tree, (12 * 1024ULL));
+}
+
 int btrfs_test_extent_map()
 {
        struct extent_map_tree *em_tree;
@@ -197,6 +270,7 @@ int btrfs_test_extent_map()
 
        test_case_1(em_tree);
        test_case_2(em_tree);
+       test_case_3(em_tree);
 
        kfree(em_tree);
        return 0;