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authorFilipe Manana <fdmanana@suse.com>2015-11-19 10:57:20 +0000
committerChris Mason <clm@fb.com>2015-11-25 05:19:51 -0800
commit020d5b7366fc03e4bf84142ae6f63031ac504e33 (patch)
tree8f2c36c78f0d213d379e172f3a824c9d90ab1b2b /fs
parentbtrfs: fix rcu warning during device replace (diff)
downloadlinux-dev-020d5b7366fc03e4bf84142ae6f63031ac504e33.tar.xz
linux-dev-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.c20
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