From 020d5b7366fc03e4bf84142ae6f63031ac504e33 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Thu, 19 Nov 2015 10:57:20 +0000 Subject: [PATCH] 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 Signed-off-by: Chris Mason --- 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 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 -- 2.30.2