From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mo-p00-ob.rzone.de ([81.169.146.160]:43402 "EHLO mo-p00-ob.rzone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750756Ab3IFIhC (ORCPT ); Fri, 6 Sep 2013 04:37:02 -0400 Message-ID: <52299420.4070702@giantdisaster.de> Date: Fri, 06 Sep 2013 10:36:48 +0200 From: Stefan Behrens MIME-Version: 1.0 To: miaox@cn.fujitsu.com CC: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] Btrfs: eliminate the exceptional root_tree refs=0 References: <6864a70d966df33d27a523d944e14f23b6594b7d.1378389401.git.sbehrens@giantdisaster.de> <52294720.8050906@cn.fujitsu.com> In-Reply-To: <52294720.8050906@cn.fujitsu.com> Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Fri, 06 Sep 2013 11:08:16 +0800, Miao Xie wrote: > On thu, 5 Sep 2013 16:58:43 +0200, Stefan Behrens wrote: >> The fact that btrfs_root_refs() returned 0 for the tree_root caused >> bugs in the past, therefore it is set to 1 with this patch and >> (hopefully) all affected code is adapted to this change. >> >> I verified this change by temporarily adding WARN_ON() checks >> everywhere where btrfs_root_refs() is used, checking whether the >> logic of the code is changed by btrfs_root_refs() returning 1 >> instead of 0 for root->root_key.objectid == BTRFS_ROOT_TREE_OBJECTID. >> With these added checks, I ran the xfstests './check -g auto'. >> >> The two roots chunk_root and log_root_tree that are only referenced >> by the superblock and the log_roots below the log_root_tree still >> have btrfs_root_refs() == 0, only the tree_root is changed. >> >> Signed-off-by: Stefan Behrens >> --- >> fs/btrfs/disk-io.c | 1 + >> fs/btrfs/inode-map.c | 3 +-- >> fs/btrfs/inode.c | 21 ++++++++------------- >> 3 files changed, 10 insertions(+), 15 deletions(-) >> >> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c >> index fa8b2c6..ffc3e43 100644 >> --- a/fs/btrfs/disk-io.c >> +++ b/fs/btrfs/disk-io.c >> @@ -2667,6 +2667,7 @@ retry_root_backup: >> >> btrfs_set_root_node(&tree_root->root_item, tree_root->node); >> tree_root->commit_root = btrfs_root_node(tree_root); >> + btrfs_set_root_refs(&tree_root->root_item, 1); >> >> location.objectid = BTRFS_EXTENT_TREE_OBJECTID; >> location.type = BTRFS_ROOT_ITEM_KEY; >> diff --git a/fs/btrfs/inode-map.c b/fs/btrfs/inode-map.c >> index 2c66ddb..d11e1c6 100644 >> --- a/fs/btrfs/inode-map.c >> +++ b/fs/btrfs/inode-map.c >> @@ -412,8 +412,7 @@ int btrfs_save_ino_cache(struct btrfs_root *root, >> return 0; >> >> /* Don't save inode cache if we are deleting this root */ >> - if (btrfs_root_refs(&root->root_item) == 0 && >> - root != root->fs_info->tree_root) >> + if (btrfs_root_refs(&root->root_item) == 0) >> return 0; >> >> if (!btrfs_test_opt(root, INODE_MAP_CACHE)) >> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c >> index 26992ee..7d0ef55 100644 >> --- a/fs/btrfs/inode.c >> +++ b/fs/btrfs/inode.c >> @@ -4472,8 +4472,10 @@ void btrfs_evict_inode(struct inode *inode) >> trace_btrfs_inode_evict(inode); >> >> truncate_inode_pages(&inode->i_data, 0); >> - if (inode->i_nlink && (btrfs_root_refs(&root->root_item) != 0 || >> - btrfs_is_free_space_inode(inode))) >> + if (inode->i_nlink && >> + ((btrfs_root_refs(&root->root_item) != 0 && >> + root->root_key.objectid != BTRFS_ROOT_TREE_OBJECTID) || >> + btrfs_is_free_space_inode(inode))) > > if (inode->i_nlink && btrfs_root_refs(&root->root_item)) { > } > > is OK, because with this patch, the refs of the free space inodes' root(tree root) > should be 1. For the ino cache inodes' root(fs/file root), if the root is dead, > we can drop the ino cache inode safely. And if the root is not dead, the refs > should be > 0, we will skip the drop. Thank you for your comments! It needs to be like this or it doesn't work. The code that you propose changes the logic when close_ctree() calls iput(fs_info->btree_inode). The if-condition in btrfs_evict_inode() used to be false for fs_info->btree_inode before this patch and would become true. And the system locks up in the middle of a './check -g auto' run with page cache issues and I have also seen the OOM killer killing the entire test box. But maybe you can propose how to make this if-statement more explicit and readable, maybe by explicitly checking for inode == fs_info->btree_inode? >> goto no_delete; >> >> if (is_bad_inode(inode)) { >> @@ -4490,7 +4492,8 @@ void btrfs_evict_inode(struct inode *inode) >> } >> >> if (inode->i_nlink > 0) { >> - BUG_ON(btrfs_root_refs(&root->root_item) != 0); >> + BUG_ON(btrfs_root_refs(&root->root_item) != 0 && >> + root->root_key.objectid != BTRFS_ROOT_TREE_OBJECTID); > > This change is unnecessary because the refs of the root tree is 1 now. Because of the thing above, this is needed. > >> goto no_delete; >> } >> >> @@ -4731,14 +4734,7 @@ static void inode_tree_del(struct inode *inode) >> } >> spin_unlock(&root->inode_lock); >> >> - /* >> - * Free space cache has inodes in the tree root, but the tree root has a >> - * root_refs of 0, so this could end up dropping the tree root as a >> - * snapshot, so we need the extra !root->fs_info->tree_root check to >> - * make sure we don't drop it. >> - */ >> - if (empty && btrfs_root_refs(&root->root_item) == 0 && >> - root != root->fs_info->tree_root) { >> + if (empty && btrfs_root_refs(&root->root_item) == 0) { >> synchronize_srcu(&root->fs_info->subvol_srcu); >> spin_lock(&root->inode_lock); >> empty = RB_EMPTY_ROOT(&root->inode_tree); >> @@ -7872,8 +7868,7 @@ int btrfs_drop_inode(struct inode *inode) >> return 1; >> >> /* the snap/subvol tree is on deleting */ >> - if (btrfs_root_refs(&root->root_item) == 0 && >> - root != root->fs_info->tree_root) >> + if (btrfs_root_refs(&root->root_item) == 0) >> return 1; >> else >> return generic_drop_inode(inode); > > The others is OK.