From: Filipe Manana <fdmanana@xxxxxxxx>
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@xxxxxxxx>
---
fs/btrfs/scrub.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 2907a77..28fbd83 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)
@@ -3577,7 +3589,7 @@ 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
--
2.1.3
--
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