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

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Date:   Mon, 28 Jan 2019 18:11:32 +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,
        Christian Brauner <christian@...uner.io>
Subject: [PATCH 1/2] devpts: remove unneeded inode_lock in mknod_ptmx

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>
---
 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