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| author | Filipe Manana <fdmanana@suse.com> | 2015-11-19 10:57:20 +0000 |
|---|---|---|
| committer | Chris Mason <clm@fb.com> | 2015-11-25 05:19:51 -0800 |
| commit | 020d5b7366fc03e4bf84142ae6f63031ac504e33 (patch) | |
| tree | 8f2c36c78f0d213d379e172f3a824c9d90ab1b2b /fs | |
| parent | 31388ab2edac833defa4193172edc1d409868bfb (diff) | |
| download | lwn-020d5b7366fc03e4bf84142ae6f63031ac504e33.tar.gz lwn-020d5b7366fc03e4bf84142ae6f63031ac504e33.zip | |
Btrfs: fix race between scrub and block group deletion
Scrub can race with the cleaner kthread deleting block groups that are
unused (and with relocation too) leading to a failure with error -EINVAL
that gets returned to user space.
The following diagram illustrates how it happens:
CPU 1 CPU 2
cleaner kthread
btrfs_delete_unused_bgs()
gets block group X from
fs_info->unused_bgs
sets block group to RO
btrfs_remove_chunk(bg X)
deletes device extents
scrub_enumerate_chunks()
searches device tree using
its commit root
finds device extent for
block group X
gets block group X from the tree
fs_info->block_group_cache_tree
(via btrfs_lookup_block_group())
sets bg X to RO (again)
btrfs_remove_block_group(bg X)
deletes block group from
fs_info->block_group_cache_tree
removes extent map from
fs_info->mapping_tree
scrub_chunk(offset X)
searches fs_info->mapping_tree
for extent map starting at
offset X
--> doesn't find any such
extent map
--> returns -EINVAL and scrub
errors out to userspace
with -EINVAL
Fix this by dealing with an extent map lookup failure as an indicator of
block group deletion.
Issue reproduced with fstest btrfs/071.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/btrfs/scrub.c | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c index 6b3fd51d9a99..68af3169d527 100644 --- a/fs/btrfs/scrub.c +++ b/fs/btrfs/scrub.c @@ -3432,7 +3432,9 @@ out: static noinline_for_stack int scrub_chunk(struct scrub_ctx *sctx, struct btrfs_device *scrub_dev, u64 chunk_offset, u64 length, - u64 dev_offset, int is_dev_replace) + u64 dev_offset, + struct btrfs_block_group_cache *cache, + int is_dev_replace) { struct btrfs_mapping_tree *map_tree = &sctx->dev_root->fs_info->mapping_tree; @@ -3445,8 +3447,18 @@ static noinline_for_stack int scrub_chunk(struct scrub_ctx *sctx, em = lookup_extent_mapping(&map_tree->map_tree, chunk_offset, 1); read_unlock(&map_tree->map_tree.lock); - if (!em) - return -EINVAL; + if (!em) { + /* + * Might have been an unused block group deleted by the cleaner + * kthread or relocation. + */ + spin_lock(&cache->lock); + if (!cache->removed) + ret = -EINVAL; + spin_unlock(&cache->lock); + + return ret; + } map = (struct map_lookup *)em->bdev; if (em->start != chunk_offset) @@ -3592,7 +3604,7 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx, dev_replace->cursor_left = found_key.offset; dev_replace->item_needs_writeback = 1; ret = scrub_chunk(sctx, scrub_dev, chunk_offset, length, - found_key.offset, is_dev_replace); + found_key.offset, cache, is_dev_replace); /* * flush, submit all pending read and write bios, afterwards |