libfs: add stashed_dentry_prune()

Both pidfs and nsfs use a memory location to stash a dentry for reuse by
concurrent openers. Right now two custom
dentry->d_prune::{ns,pidfs}_prune_dentry() methods are needed that do
the same thing. The only thing that differs is that they need to get to
the memory location to store or retrieve the dentry from differently.
Fix that by remember the stashing location for the dentry in
dentry->d_fsdata which allows us to retrieve it in dentry->d_prune. That
in turn makes it possible to add a common helper that pidfs and nsfs can
both use.

Link: https://lore.kernel.org/r/CAHk-=wg8cHY=i3m6RnXQ2Y2W8psicKWQEZq1=94ivUiviM-0OA@mail.gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 2 insertions, 14 deletions

diff --git a/fs/nsfs.c b/fs/nsfs.c
index 3a36bb62353c..2ce229af34e9 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -34,22 +34,10 @@ static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
 		ns_ops->name, inode->i_ino);
 }
 
-static void ns_prune_dentry(struct dentry *dentry)
-{
-	struct inode *inode;
-
-	inode = d_inode(dentry);
-	if (inode) {
-		struct ns_common *ns = inode->i_private;
-		cmpxchg(&ns->stashed, dentry, NULL);
-	}
-}
-
-const struct dentry_operations ns_dentry_operations =
-{
-	.d_prune	= ns_prune_dentry,
+const struct dentry_operations ns_dentry_operations = {
 	.d_delete	= always_delete_dentry,
 	.d_dname	= ns_dname,
+	.d_prune	= stashed_dentry_prune,
 };
 
 static void nsfs_evict(struct inode *inode)