[PATCH 1/2] devpts: remove unneeded inode_lock in mknod_ptmx

[PATCH 1/2] devpts: remove unneeded inode_lock in mknod_ptmx

[Christian Brauner]

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@zeniv.linux.org.uk>
Signed-off-by: Christian Brauner <christian@brauner.io>
---
 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

[PATCH 2/2] devpts: simplify devpts_fill_super()

[Christian Brauner]

When devpts_fill_super() fails deactivate_locked_super() will cleanup
dentries for us so there's no need to do that work in devpts_fill_super()
itself. This allows us to simplify that function quite a bit.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Christian Brauner <christian@brauner.io>
---
 fs/devpts/inode.c | 22 ++++++----------------
 1 file changed, 6 insertions(+), 16 deletions(-)

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 8fa1492f9712..59b7625a2110 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -450,19 +450,18 @@ devpts_fill_super(struct super_block *s, void *data, int silent)
 	s->s_op = &devpts_sops;
 	s->s_time_gran = 1;
 
-	error = -ENOMEM;
 	s->s_fs_info = new_pts_fs_info(s);
 	if (!s->s_fs_info)
-		goto fail;
+		return -ENOMEM;
 
 	error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
 	if (error)
-		goto fail;
+		return error;
 
-	error = -ENOMEM;
 	inode = new_inode(s);
 	if (!inode)
-		goto fail;
+		return -ENOMEM;
+
 	inode->i_ino = 1;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
 	inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
@@ -473,19 +472,10 @@ devpts_fill_super(struct super_block *s, void *data, int silent)
 	s->s_root = d_make_root(inode);
 	if (!s->s_root) {
 		pr_err("get root dentry failed\n");
-		goto fail;
+		return -ENOMEM;
 	}
 
-	error = mknod_ptmx(s);
-	if (error)
-		goto fail_dput;
-
-	return 0;
-fail_dput:
-	dput(s->s_root);
-	s->s_root = NULL;
-fail:
-	return error;
+	return mknod_ptmx(s);
 }
 
 /*
-- 
2.20.1

Re: [PATCH 1/2] devpts: remove unneeded inode_lock in mknod_ptmx

[Christian Brauner]

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@zeniv.linux.org.uk>
> Signed-off-by: Christian Brauner <christian@brauner.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
>