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..4e2461b8 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -4753,6 +4753,7 @@
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 @@
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 @@
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 @@
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);
}
/*