[PATCH] exportfs: remove locking around ->get_parent() call.

[PATCH] exportfs: remove locking around ->get_parent() call.

[NeilBrown]

The locking around the ->get_parent() call brings no value.
We are locking a child which is only used to find an inode and thence the
parent inode number.  All further activity involves the parent inode
which may have several children so locking one child cannot protect the
parent in any useful way.

The filesystem must already ensure that only one 'struct inode' exists
for a given inode, and will call d_obtain_alias() which contains the
required locking to ensure only one dentry will be attached to that
inode.

So remove the unnecessary locking.

Signed-off-by: NeilBrown <neil@brown.name>
---

I've been reviewing locking in directories and this stood out has
unnecessary.  It isn't harmful, but it doesn't bring any value.
NeilBrown


 fs/exportfs/expfs.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index 0c899cfba578..b5845c4846b8 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -126,10 +126,8 @@ static struct dentry *reconnect_one(struct vfsmount *mnt,
 	int err;
 
 	parent = ERR_PTR(-EACCES);
-	inode_lock(dentry->d_inode);
 	if (mnt->mnt_sb->s_export_op->get_parent)
 		parent = mnt->mnt_sb->s_export_op->get_parent(dentry);
-	inode_unlock(dentry->d_inode);
 
 	if (IS_ERR(parent)) {
 		dprintk("get_parent of %lu failed, err %ld\n",
-- 
2.48.1

Re: [PATCH] exportfs: remove locking around ->get_parent() call.

[Christian Brauner]

On Fri, 14 Mar 2025 09:29:33 +1100, NeilBrown wrote:
> The locking around the ->get_parent() call brings no value.
> We are locking a child which is only used to find an inode and thence the
> parent inode number.  All further activity involves the parent inode
> which may have several children so locking one child cannot protect the
> parent in any useful way.
> 
> The filesystem must already ensure that only one 'struct inode' exists
> for a given inode, and will call d_obtain_alias() which contains the
> required locking to ensure only one dentry will be attached to that
> inode.
> 
> [...]

Applied to the vfs-6.15.misc branch of the vfs/vfs.git tree.
Patches in the vfs-6.15.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.15.misc

[1/1] exportfs: remove locking around ->get_parent() call.
      https://git.kernel.org/vfs/vfs/c/64a56f635aae