On 22.12.2017 00:42, Liu Bo wrote:
> This test case simulates the racy situation of buffered write vs dio
> read, and see if btrfs_get_extent() would return -EEXIST.
Isn't mixing dio/buffered IO on the same file (range?) considered
dangerous in any case?
>
> Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> ---
> fs/btrfs/tests/extent-map-tests.c | 73 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 73 insertions(+)
>
> diff --git a/fs/btrfs/tests/extent-map-tests.c b/fs/btrfs/tests/extent-map-tests.c
> index 0407396..2adf55f 100644
> --- a/fs/btrfs/tests/extent-map-tests.c
> +++ b/fs/btrfs/tests/extent-map-tests.c
> @@ -181,6 +181,78 @@ static void test_case_2(struct extent_map_tree *em_tree)
> 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;
> @@ -196,6 +268,7 @@ 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;
>
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