Btrfs: add extent map selftests

We've observed that btrfs_get_extent() and merge_extent_mapping() could
return -EEXIST in several cases, and they are caused by some racy
condition, e.g dio read vs dio write, which makes the problem very tricky
to reproduce.

This adds extent map selftests in order to simulate those racy situations.

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

fs/btrfs/Makefile

@@ -19,4 +19,4 @@ btrfs-$(CONFIG_BTRFS_FS_REF_VERIFY) += ref-verify.o
 btrfs-$(CONFIG_BTRFS_FS_RUN_SANITY_TESTS) += tests/free-space-tests.o \
 	tests/extent-buffer-tests.o tests/btrfs-tests.o \
 	tests/extent-io-tests.o tests/inode-tests.o tests/qgroup-tests.o \
-	tests/free-space-tree-tests.o
+	tests/free-space-tree-tests.o tests/extent-map-tests.o

fs/btrfs/tests/btrfs-tests.c

@@ -277,6 +277,9 @@ int btrfs_run_sanity_tests(void)
 				goto out;
 		}
 	}
+	ret = btrfs_test_extent_map();
+	if (ret)
+		goto out;
 out:
 	btrfs_destroy_test_fs();
 	return ret;

fs/btrfs/tests/btrfs-tests.h

@@ -33,6 +33,7 @@ int btrfs_test_extent_io(u32 sectorsize, u32 nodesize);
 int btrfs_test_inodes(u32 sectorsize, u32 nodesize);
 int btrfs_test_qgroups(u32 sectorsize, u32 nodesize);
 int btrfs_test_free_space_tree(u32 sectorsize, u32 nodesize);
+int btrfs_test_extent_map(void);
 struct inode *btrfs_new_test_inode(void);
 struct btrfs_fs_info *btrfs_alloc_dummy_fs_info(u32 nodesize, u32 sectorsize);
 void btrfs_free_dummy_fs_info(struct btrfs_fs_info *fs_info);

fs/btrfs/tests/extent-map-tests.c

@@ -0,0 +1,203 @@
+/*
+ * Copyright (C) 2017 Oracle.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#include <linux/types.h>
+#include "btrfs-tests.h"
+#include "../ctree.h"
+
+static void free_extent_map_tree(struct extent_map_tree *em_tree)
+{
+	struct extent_map *em;
+	struct rb_node *node;
+
+	while (!RB_EMPTY_ROOT(&em_tree->map)) {
+		node = rb_first(&em_tree->map);
+		em = rb_entry(node, struct extent_map, rb_node);
+		remove_extent_mapping(em_tree, em);
+
+#ifdef CONFIG_BTRFS_DEBUG
+		if (refcount_read(&em->refs) != 1) {
+			test_msg(
+"em leak: em (start 0x%llx len 0x%llx block_start 0x%llx block_len 0x%llx) refs %d\n",
+				 em->start, em->len, em->block_start,
+				 em->block_len, refcount_read(&em->refs));
+
+			refcount_set(&em->refs, 1);
+		}
+#endif
+		free_extent_map(em);
+	}
+}
+
+/*
+ * Test scenario:
+ *
+ * Suppose that no extent map has been loaded into memory yet, there is a file
+ * extent [0, 16K), followed by another file extent [16K, 20K), two dio reads
+ * are entering btrfs_get_extent() concurrently, t1 is reading [8K, 16K), t2 is
+ * reading [0, 8K)
+ *
+ *     t1                            t2
+ *  btrfs_get_extent()              btrfs_get_extent()
+ *    -> lookup_extent_mapping()      ->lookup_extent_mapping()
+ *    -> add_extent_mapping(0, 16K)
+ *    -> return em
+ *                                    ->add_extent_mapping(0, 16K)
+ *                                    -> #handle -EEXIST
+ */
+static void test_case_1(struct extent_map_tree *em_tree)
+{
+	struct extent_map *em;
+	u64 start = 0;
+	u64 len = SZ_8K;
+	int ret;
+
+	em = alloc_extent_map();
+	if (!em)
+		/* Skip the test on error. */
+		return;
+
+	/* Add [0, 16K) */
+	em->start = 0;
+	em->len = SZ_16K;
+	em->block_start = 0;
+	em->block_len = SZ_16K;
+	ret = add_extent_mapping(em_tree, em, 0);
+	ASSERT(ret == 0);
+	free_extent_map(em);
+
+	/* Add [16K, 20K) following [0, 16K)  */
+	em = alloc_extent_map();
+	if (!em)
+		goto out;
+
+	em->start = SZ_16K;
+	em->len = SZ_4K;
+	em->block_start = SZ_32K; /* avoid merging */
+	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, 8K), should return [0, 16K) instead. */
+	em->start = start;
+	em->len = len;
+	em->block_start = start;
+	em->block_len = len;
+	ret = btrfs_add_extent_mapping(em_tree, &em, em->start, em->len);
+	if (ret)
+		test_msg("case1 [%llu %llu]: ret %d\n", start, start + len, ret);
+	if (em &&
+	    (em->start != 0 || extent_map_end(em) != SZ_16K ||
+	     em->block_start != 0 || em->block_len != SZ_16K))
+		test_msg(
+"case1 [%llu %llu]: ret %d return a wrong em (start %llu len %llu block_start %llu block_len %llu\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:
+ *
+ * Reading the inline ending up with EEXIST, ie. read an inline
+ * extent and discard page cache and read it again.
+ */
+static void test_case_2(struct extent_map_tree *em_tree)
+{
+	struct extent_map *em;
+	int ret;
+
+	em = alloc_extent_map();
+	if (!em)
+		/* Skip the test on error. */
+		return;
+
+	/* Add [0, 1K) */
+	em->start = 0;
+	em->len = SZ_1K;
+	em->block_start = EXTENT_MAP_INLINE;
+	em->block_len = (u64)-1;
+	ret = add_extent_mapping(em_tree, em, 0);
+	ASSERT(ret == 0);
+	free_extent_map(em);
+
+	/* Add [4K, 4K) following [0, 1K)  */
+	em = alloc_extent_map();
+	if (!em)
+		goto out;
+
+	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, 1K) */
+	em->start = 0;
+	em->len = SZ_1K;
+	em->block_start = EXTENT_MAP_INLINE;
+	em->block_len = (u64)-1;
+	ret = btrfs_add_extent_mapping(em_tree, &em, em->start, em->len);
+	if (ret)
+		test_msg("case2 [0 1K]: ret %d\n", ret);
+	if (em &&
+	    (em->start != 0 || extent_map_end(em) != SZ_1K ||
+	     em->block_start != EXTENT_MAP_INLINE || em->block_len != (u64)-1))
+		test_msg(
+"case2 [0 1K]: ret %d return a wrong em (start %llu len %llu block_start %llu block_len %llu\n",
+			 ret, em->start, em->len, em->block_start,
+			 em->block_len);
+	free_extent_map(em);
+out:
+	/* free memory */
+	free_extent_map_tree(em_tree);
+}
+
+int btrfs_test_extent_map()
+{
+	struct extent_map_tree *em_tree;
+
+	test_msg("Running extent_map tests\n");
+
+	em_tree = kzalloc(sizeof(*em_tree), GFP_KERNEL);
+	if (!em_tree)
+		/* Skip the test on error. */
+		return 0;
+
+	extent_map_tree_init(em_tree);
+
+	test_case_1(em_tree);
+	test_case_2(em_tree);
+
+	kfree(em_tree);
+	return 0;
+}