linux-kernel - Re: [V2] btrfs: drop inode reference count on error path

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Date:   Thu, 18 Apr 2019 10:11:35 -0400
From:   Josef Bacik <josef@...icpanda.com>
To:     Nikolay Borisov <nborisov@...e.com>
Cc:     Josef Bacik <josef@...icpanda.com>, Pan Bian <bianpan2016@....com>,
        Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [V2] btrfs: drop inode reference count on error path

On Thu, Apr 18, 2019 at 05:09:44PM +0300, Nikolay Borisov wrote:
> 
> 
> On 18.04.19 г. 17:07 ч., Josef Bacik wrote:
> > On Thu, Apr 18, 2019 at 03:50:00PM +0300, Nikolay Borisov wrote:
> >>
> >>
> >> On 18.04.19 г. 14:06 ч., Pan Bian wrote:
> >>> The reference count of inode is incremented by ihold. It should be
> >>> dropped if not used. However, the reference count is not dropped if
> >>> error occurs during updating the inode or deleting orphan items. This
> >>> patch fixes the bug.
> >>>
> >>> Signed-off-by: Pan Bian <bianpan2016@....com>
> >>> ---
> >>> V2: move ihold just before device_initialize to make code clearer
> >>> ---
> >>>  fs/btrfs/inode.c | 54 +++++++++++++++++++++++++-----------------------------
> >>>  1 file changed, 25 insertions(+), 29 deletions(-)
> >>>
> >>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> >>> index 82fdda8..d6630df 100644
> >>> --- a/fs/btrfs/inode.c
> >>> +++ b/fs/btrfs/inode.c
> >>> @@ -6579,7 +6579,7 @@ static int btrfs_link(struct dentry *old_dentry, struct inode *dir,
> >>>  	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> >>>  	u64 index;
> >>>  	int err;
> >>> -	int drop_inode = 0;
> >>> +	int log_mode;
> >>>  
> >>>  	/* do not allow sys_link's with other subvols of the same device */
> >>>  	if (root->root_key.objectid != BTRFS_I(inode)->root->root_key.objectid)
> >>> @@ -6616,41 +6616,37 @@ static int btrfs_link(struct dentry *old_dentry, struct inode *dir,
> >>>  	err = btrfs_add_nondir(trans, BTRFS_I(dir), dentry, BTRFS_I(inode),
> >>>  			1, index);
> >>>  
> >>> -	if (err) {
> >>> -		drop_inode = 1;
> >>> -	} else {
> >>> -		struct dentry *parent = dentry->d_parent;
> >>> -		int ret;
> >>> +	if (err)
> >>> +		goto err_link;
> >>>  
> >>> -		err = btrfs_update_inode(trans, root, inode);
> >>> +	err = btrfs_update_inode(trans, root, inode);
> >>> +	if (err)
> >>> +		goto err_link;
> >>> +	if (inode->i_nlink == 1) {
> >>> +		/*
> >>> +		 * If new hard link count is 1, it's a file created
> >>> +		 * with open(2) O_TMPFILE flag.
> >>> +		 */
> >>> +		err = btrfs_orphan_del(trans, BTRFS_I(inode));
> >>>  		if (err)
> >>> -			goto fail;
> >>> -		if (inode->i_nlink == 1) {
> >>> -			/*
> >>> -			 * If new hard link count is 1, it's a file created
> >>> -			 * with open(2) O_TMPFILE flag.
> >>> -			 */
> >>> -			err = btrfs_orphan_del(trans, BTRFS_I(inode));
> >>> -			if (err)
> >>> -				goto fail;
> >>> -		}
> >>> -		BTRFS_I(inode)->last_link_trans = trans->transid;
> >>> -		d_instantiate(dentry, inode);
> >>> -		ret = btrfs_log_new_name(trans, BTRFS_I(inode), NULL, parent,
> >>> -					 true, NULL);
> >>> -		if (ret == BTRFS_NEED_TRANS_COMMIT) {
> >>> -			err = btrfs_commit_transaction(trans);
> >>> -			trans = NULL;
> >>> -		}
> >>> +			goto err_link;
> >>> +	}
> >>> +	BTRFS_I(inode)->last_link_trans = trans->transid;
> >>> +	ihold(inode);
> > 
> > Where is the iput for this ihold?
> 
> This ihold is sort of "given" to the d_instantiate. I.e the iput happens
> when the respective dentry is unhashed/removed.

Ah that's what I was missing, thanks,

Josef