On Fri, Dec 22, 2017 at 09:42:17AM +0200, Nikolay Borisov wrote:
>
>
> On 22.12.2017 00:42, Liu Bo wrote:
> > 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@xxxxxxxxxx>
> > ---
> > fs/btrfs/Makefile | 2 +-
> > fs/btrfs/tests/btrfs-tests.c | 3 +
> > fs/btrfs/tests/btrfs-tests.h | 1 +
> > fs/btrfs/tests/extent-map-tests.c | 202 ++++++++++++++++++++++++++++++++++++++
> > 4 files changed, 207 insertions(+), 1 deletion(-)
> > create mode 100644 fs/btrfs/tests/extent-map-tests.c
> >
> > diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
> > index 6fe881d..0c43736 100644
> > --- a/fs/btrfs/Makefile
> > +++ b/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
> > diff --git a/fs/btrfs/tests/btrfs-tests.c b/fs/btrfs/tests/btrfs-tests.c
> > index d3f2537..9786d8c 100644
> > --- a/fs/btrfs/tests/btrfs-tests.c
> > +++ b/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;
> > diff --git a/fs/btrfs/tests/btrfs-tests.h b/fs/btrfs/tests/btrfs-tests.h
> > index 266f1e3..bc0615b 100644
> > --- a/fs/btrfs/tests/btrfs-tests.h
> > +++ b/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);
> > diff --git a/fs/btrfs/tests/extent-map-tests.c b/fs/btrfs/tests/extent-map-tests.c
> > new file mode 100644
> > index 0000000..0407396
> > --- /dev/null
> > +++ b/fs/btrfs/tests/extent-map-tests.c
> > @@ -0,0 +1,202 @@
> > +/*
> > + * 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(
> > + "Oops we have a 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)
> > +{
>
> So here you are testing the "fully overlapping" case in btrfs_add_extent_mapping.
> What about another test case about merging 2 adjacent extents i.e. this block of code:
>
> } else if (start >= extent_map_end(existing) || start <= existing->start) {
>
They're in the following patches.
> > + 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;
>
> Any particular reason you are using start/len and not the constants as in the
> previous 2 extent insertion cases? Makes it a lot easier to see what's happening
> without reading the above variables?
>
The above comment showed it, didn't it?
The following if (ret) and if (em...) also uses start and len.
thanks,
-liubo
> > + 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;
> > +}
> >
> --
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