Btrfs: fix protection between send and root deletion

We should gurantee that parent and clone roots can not be destroyed
during send, for this we have two ideas.

1.by holding @subvol_sem, this might be a nightmare, because it will
block all subvolumes deletion for a long time.

2.Miao pointed out we can reuse @send_in_progress, that mean we will
skip snapshot deletion if root sending is in progress.

Here we adopt the second approach since it won't block other subvolumes
deletion for a long time.

Besides in btrfs_clean_one_deleted_snapshot(), we only check first root
, if this root is involved in send, we return directly rather than
continue to check.There are several reasons about it:

1.this case happen seldomly.
2.after sending,cleaner thread can continue to drop that root.
3.make code simple

Cc: David Sterba <dsterba@suse.cz>
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Reviewed-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 5b69785..4e2461b 100644 (file)
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -4753,6 +4753,7 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
        u64 *clone_sources_tmp = NULL;
        int clone_sources_to_rollback = 0;
        int sort_clone_roots = 0;
+       int index;
 
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
@@ -4893,8 +4894,12 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
                        key.objectid = clone_sources_tmp[i];
                        key.type = BTRFS_ROOT_ITEM_KEY;
                        key.offset = (u64)-1;
+
+                       index = srcu_read_lock(&fs_info->subvol_srcu);
+
                        clone_root = btrfs_read_fs_root_no_name(fs_info, &key);
                        if (IS_ERR(clone_root)) {
+                               srcu_read_unlock(&fs_info->subvol_srcu, index);
                                ret = PTR_ERR(clone_root);
                                goto out;
                        }
@@ -4903,10 +4908,13 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
                        clone_root->send_in_progress++;
                        if (!btrfs_root_readonly(clone_root)) {
                                spin_unlock(&clone_root->root_item_lock);
+                               srcu_read_unlock(&fs_info->subvol_srcu, index);
                                ret = -EPERM;
                                goto out;
                        }
                        spin_unlock(&clone_root->root_item_lock);
+                       srcu_read_unlock(&fs_info->subvol_srcu, index);
+
                        sctx->clone_roots[i].root = clone_root;
                }
                vfree(clone_sources_tmp);
@@ -4917,19 +4925,27 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
                key.objectid = arg->parent_root;
                key.type = BTRFS_ROOT_ITEM_KEY;
                key.offset = (u64)-1;
+
+               index = srcu_read_lock(&fs_info->subvol_srcu);
+
                sctx->parent_root = btrfs_read_fs_root_no_name(fs_info, &key);
                if (IS_ERR(sctx->parent_root)) {
+                       srcu_read_unlock(&fs_info->subvol_srcu, index);
                        ret = PTR_ERR(sctx->parent_root);
                        goto out;
                }
+
                spin_lock(&sctx->parent_root->root_item_lock);
                sctx->parent_root->send_in_progress++;
                if (!btrfs_root_readonly(sctx->parent_root)) {
                        spin_unlock(&sctx->parent_root->root_item_lock);
+                       srcu_read_unlock(&fs_info->subvol_srcu, index);
                        ret = -EPERM;
                        goto out;
                }
                spin_unlock(&sctx->parent_root->root_item_lock);
+
+               srcu_read_unlock(&fs_info->subvol_srcu, index);
        }
 
        /*

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index e5fe801..da2ac4c 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1972,6 +1972,19 @@ int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root)
        }
        root = list_first_entry(&fs_info->dead_roots,
                        struct btrfs_root, root_list);
+       /*
+        * Make sure root is not involved in send,
+        * if we fail with first root, we return
+        * directly rather than continue.
+        */
+       spin_lock(&root->root_item_lock);
+       if (root->send_in_progress) {
+               spin_unlock(&fs_info->trans_lock);
+               spin_unlock(&root->root_item_lock);
+               return 0;
+       }
+       spin_unlock(&root->root_item_lock);
+
        list_del_init(&root->root_list);
        spin_unlock(&fs_info->trans_lock);