From 18f687d538449373c37cbe52b03f5f3d42b7c7ed Mon Sep 17 00:00:00 2001 From: Wang Shilong Date: Tue, 7 Jan 2014 17:25:19 +0800 Subject: [PATCH] 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 Signed-off-by: Wang Shilong Reviewed-by: Miao Xie Signed-off-by: Josef Bacik Signed-off-by: Chris Mason --- fs/btrfs/send.c | 16 ++++++++++++++++ fs/btrfs/transaction.c | 13 +++++++++++++ 2 files changed, 29 insertions(+) diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c index 5b69785..4e2461b 100644 --- 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 --- 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); -- 2.7.4