Re: [PATCH 04/10] Btrfs: extent map selftest: buffered write vs dio read

[Liu Bo]

On Fri, Dec 22, 2017 at 09:51:24AM +0200, Nikolay Borisov wrote:
> 
> 
> 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?

They are, but it is sometimes the way how applications work.

thanks,
-liubo

> 
> > 
> > Signed-off-by: Liu Bo 
> > ---
> >  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, , 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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Re: [PATCH 04/10] Btrfs: extent map selftest: buffered write vs dio read

[Nikolay Borisov]

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 
> ---
>  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, , 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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