path: root/fs/btrfs/scrub.c
diff options
authorFilipe Manana <fdmanana@suse.com>2015-11-19 11:45:48 +0000
committerChris Mason <clm@fb.com>2015-11-25 05:22:08 -0800
commit758f2dfcf8a249b1f1510aa32e625c2ec20642a3 (patch)
treea521154fb1e3384087e4a828197f69eca158d280 /fs/btrfs/scrub.c
parentBtrfs: fix race between scrub and block group deletion (diff)
Btrfs: fix scrub preventing unused block groups from being deleted
Currently scrub can race with the cleaner kthread when the later attempts to delete an unused block group, and the result is preventing the cleaner kthread from ever deleting later the block group - unless the block group becomes used and unused again. The following diagram illustrates that race: CPU 1 CPU 2 cleaner kthread btrfs_delete_unused_bgs() gets block group X from fs_info->unused_bgs and removes it from that list 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 sees the block group is already RO and therefore doesn't delete it nor adds it back to unused list So fix this by making scrub add the block group again to the list of unused block groups if the block group is still unused when it finished scrubbing it and it hasn't been removed already. Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
Diffstat (limited to '')
1 files changed, 22 insertions, 0 deletions
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 68af3169d527..b091d94ceef6 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3641,6 +3641,28 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
if (ro_set)
btrfs_dec_block_group_ro(root, cache);
+ /*
+ * We might have prevented the cleaner kthread from deleting
+ * this block group if it was already unused because we raced
+ * and set it to RO mode first. So add it back to the unused
+ * list, otherwise it might not ever be deleted unless a manual
+ * balance is triggered or it becomes used and unused again.
+ */
+ spin_lock(&cache->lock);
+ if (!cache->removed && !cache->ro && cache->reserved == 0 &&
+ btrfs_block_group_used(&cache->item) == 0) {
+ spin_unlock(&cache->lock);
+ spin_lock(&fs_info->unused_bgs_lock);
+ if (list_empty(&cache->bg_list)) {
+ btrfs_get_block_group(cache);
+ list_add_tail(&cache->bg_list,
+ &fs_info->unused_bgs);
+ }
+ spin_unlock(&fs_info->unused_bgs_lock);
+ } else {
+ spin_unlock(&cache->lock);
+ }
if (ret)