binderfs: drop lock in binderfs_binder_ctl_create

This change “binderfs: drop lock in binderfs_binder_ctl_create” in Linux kernel is authored by Christian Brauner <christian [at] brauner.io> on Mon Jan 21 11:48:07 2019 +0100.

binderfs: drop lock in binderfs_binder_ctl_create

The binderfs_binder_ctl_create() call is a no-op on subsequent calls and
the first call is done before we unlock the suberblock. Hence, there is no
need to take inode_lock() in there. Let's remove it.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Christian Brauner <christian@brauner.io>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit 29ef1c8.

There are 4 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/android/binderfs.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index ba88be1..d537dcd 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -400,8 +400,6 @@ static int binderfs_binder_ctl_create(struct super_block *sb)
 	if (!device)
 		return -ENOMEM;
 
-	inode_lock(d_inode(root));
-
 	/* If we have already created a binder-control node, return. */
 	if (info->control_dentry) {
 		ret = 0;
@@ -440,12 +438,10 @@ static int binderfs_binder_ctl_create(struct super_block *sb)
 	inode->i_private = device;
 	info->control_dentry = dentry;
 	d_add(dentry, inode);
-	inode_unlock(d_inode(root));
 
 	return 0;
 
 out:
-	inode_unlock(d_inode(root));
 	kfree(device);
 	iput(inode);
 

The commit for this change in Linux stable tree is 29ef1c8 (patch).

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