linux-kernel - Re: [PATCH 1/2] devpts: remove unneeded inode_lock in mknod

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Message-ID: <20190219092410.ottcfwsgt7734vx7@brauner.io>
Date:   Tue, 19 Feb 2019 10:24:11 +0100
From:   Christian Brauner <christian@...uner.io>
To:     linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org
Cc:     gregkh@...uxfoundation.org, ebiederm@...ssion.com,
        ebiggers@...gle.com, willy@...radead.org, dhowells@...hat.com
Subject: Re: [PATCH 1/2] devpts: remove unneeded inode_lock in mknod_ptmx

On Mon, Jan 28, 2019 at 06:11:32PM +0100, Christian Brauner wrote:
> Afaict, the mknod_ptmx() call is a no-op on subsequent calls and the first
> call is done before we unlock the suberblock. If I'm not mistaken this is
> exactly parallel to what Al pointed out for binderfs 29ef1c8e16a
> ("binderfs: drop lock in binderfs_binder_ctl_create"). In both filesystems
> it should not be necessary to take inode_lock() in there. Let's remove it
> and remove the goto.
> 
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Christian Brauner <christian@...uner.io>

Since the merge window is coming up: are you fine with this patch, Al?

Christian

> ---
>  fs/devpts/inode.c | 19 ++++++-------------
>  1 file changed, 6 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
> index c53814539070..8fa1492f9712 100644
> --- a/fs/devpts/inode.c
> +++ b/fs/devpts/inode.c
> @@ -325,7 +325,6 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
>  static int mknod_ptmx(struct super_block *sb)
>  {
>  	int mode;
> -	int rc = -ENOMEM;
>  	struct dentry *dentry;
>  	struct inode *inode;
>  	struct dentry *root = sb->s_root;
> @@ -334,18 +333,14 @@ static int mknod_ptmx(struct super_block *sb)
>  	kuid_t ptmx_uid = current_fsuid();
>  	kgid_t ptmx_gid = current_fsgid();
>  
> -	inode_lock(d_inode(root));
> -
>  	/* If we have already created ptmx node, return */
> -	if (fsi->ptmx_dentry) {
> -		rc = 0;
> -		goto out;
> -	}
> +	if (fsi->ptmx_dentry)
> +		return 0;
>  
>  	dentry = d_alloc_name(root, "ptmx");
>  	if (!dentry) {
>  		pr_err("Unable to alloc dentry for ptmx node\n");
> -		goto out;
> +		return -ENOMEM;
>  	}
>  
>  	/*
> @@ -355,7 +350,7 @@ static int mknod_ptmx(struct super_block *sb)
>  	if (!inode) {
>  		pr_err("Unable to alloc inode for ptmx node\n");
>  		dput(dentry);
> -		goto out;
> +		return -ENOMEM;
>  	}
>  
>  	inode->i_ino = 2;
> @@ -369,10 +364,8 @@ static int mknod_ptmx(struct super_block *sb)
>  	d_add(dentry, inode);
>  
>  	fsi->ptmx_dentry = dentry;
> -	rc = 0;
> -out:
> -	inode_unlock(d_inode(root));
> -	return rc;
> +
> +	return 0;
>  }
>  
>  static void update_ptmx_mode(struct pts_fs_info *fsi)
> -- 
> 2.20.1
>