1 files changed, 40 insertions, 1 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3f43bfea3684..a9aadb2ad525 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1751,6 +1751,7 @@ static int cleaner_kthread(void *arg)
 {
         struct btrfs_root *root = arg;
         int again;
+        struct btrfs_trans_handle *trans;
 
         do {
                 again = 0;
@@ -1772,7 +1773,6 @@ static int cleaner_kthread(void *arg)
                 }
 
                 btrfs_run_delayed_iputs(root);
-                btrfs_delete_unused_bgs(root->fs_info);
                 again = btrfs_clean_one_deleted_snapshot(root);
                 mutex_unlock(&root->fs_info->cleaner_mutex);
 
@@ -1781,6 +1781,16 @@ static int cleaner_kthread(void *arg)
                  * needn't do anything special here.
                  */
                 btrfs_run_defrag_inodes(root->fs_info);
+
+                /*
+                 * Acquires fs_info->delete_unused_bgs_mutex to avoid racing
+                 * with relocation (btrfs_relocate_chunk) and relocation
+                 * acquires fs_info->cleaner_mutex (btrfs_relocate_block_group)
+                 * after acquiring fs_info->delete_unused_bgs_mutex. So we
+                 * can't hold, nor need to, fs_info->cleaner_mutex when deleting
+                 * unused block groups.
+                 */
+                btrfs_delete_unused_bgs(root->fs_info);
 sleep:
                 if (!try_to_freeze() && !again) {
                         set_current_state(TASK_INTERRUPTIBLE);
@@ -1789,6 +1799,34 @@ sleep:
                         __set_current_state(TASK_RUNNING);
                 }
         } while (!kthread_should_stop());
+
+        /*
+         * Transaction kthread is stopped before us and wakes us up.
+         * However we might have started a new transaction and COWed some
+         * tree blocks when deleting unused block groups for example. So
+         * make sure we commit the transaction we started to have a clean
+         * shutdown when evicting the btree inode - if it has dirty pages
+         * when we do the final iput() on it, eviction will trigger a
+         * writeback for it which will fail with null pointer dereferences
+         * since work queues and other resources were already released and
+         * destroyed by the time the iput/eviction/writeback is made.
+         */
+        trans = btrfs_attach_transaction(root);
+        if (IS_ERR(trans)) {
+                if (PTR_ERR(trans) != -ENOENT)
+                        btrfs_err(root->fs_info,
+                                  "cleaner transaction attach returned %ld",
+                                  PTR_ERR(trans));
+        } else {
+                int ret;
+
+                ret = btrfs_commit_transaction(trans, root);
+                if (ret)
+                        btrfs_err(root->fs_info,
+                                  "cleaner open transaction commit returned %d",
+                                  ret);
+        }
+
         return 0;
 }
 
@@ -2492,6 +2530,7 @@ int open_ctree(struct super_block *sb,
         spin_lock_init(&fs_info->unused_bgs_lock);
         rwlock_init(&fs_info->tree_mod_log_lock);
         mutex_init(&fs_info->unused_bg_unpin_mutex);
+        mutex_init(&fs_info->delete_unused_bgs_mutex);
         mutex_init(&fs_info->reloc_mutex);
         mutex_init(&fs_info->delalloc_root_mutex);
         seqlock_init(&fs_info->profiles_lock);