linux-kernel - [RFC PATCH v3 18/59] struct filename ->refcnt doesn't need to be atomic

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Message-ID: <20251216035518.4037331-19-viro@zeniv.linux.org.uk>
Date: Tue, 16 Dec 2025 03:54:37 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: linux-fsdevel@...r.kernel.org
Cc: torvalds@...ux-foundation.org,
	brauner@...nel.org,
	jack@...e.cz,
	mjguzik@...il.com,
	paul@...l-moore.com,
	axboe@...nel.dk,
	audit@...r.kernel.org,
	io-uring@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH v3 18/59] struct filename ->refcnt doesn't need to be atomic

... or visible outside of audit, really.  Note that references
held in delayed_filename always have refcount 1, and from the
moment of complete_getname() or equivalent point in getname...()
there won't be any references to struct filename instance left
in places visible to other threads.

Acked-by: Paul Moore <paul@...l-moore.com>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 fs/namei.c         | 10 +++++-----
 include/linux/fs.h |  8 +-------
 kernel/auditsc.c   |  6 ++++++
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 4faaae0239ad..192d31acb4ff 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -150,7 +150,7 @@ static inline void free_filename(struct filename *p)
 static inline void initname(struct filename *name)
 {
 	name->aname = NULL;
-	atomic_set(&name->refcnt, 1);
+	name->refcnt = 1;
 }
 
 static int getname_long(struct filename *name, const char __user *filename)
@@ -294,13 +294,13 @@ void putname(struct filename *name)
 	if (IS_ERR_OR_NULL(name))
 		return;
 
-	refcnt = atomic_read(&name->refcnt);
+	refcnt = name->refcnt;
 	if (unlikely(refcnt != 1)) {
 		if (WARN_ON_ONCE(!refcnt))
 			return;
 
-		if (!atomic_dec_and_test(&name->refcnt))
-			return;
+		name->refcnt--;
+		return;
 	}
 
 	if (unlikely(name->name != name->iname))
@@ -332,7 +332,7 @@ int putname_to_delayed(struct delayed_filename *v, struct filename *__name)
 {
 	struct filename *name __free(putname) = no_free_ptr(__name);
 
-	if (likely(atomic_read(&name->refcnt) == 1)) {
+	if (likely(name->refcnt == 1)) {
 		v->__incomplete_filename = no_free_ptr(name);
 		return 0;
 	}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e446cb8c1e37..b711f46ba8f5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2412,7 +2412,7 @@ struct audit_names;
 
 struct __filename_head {
 	const char		*name;	/* pointer to actual string */
-	atomic_t		refcnt;
+	int			refcnt;
 	struct audit_names	*aname;
 };
 #define EMBEDDED_NAME_MAX	192 - sizeof(struct __filename_head)
@@ -2527,12 +2527,6 @@ void dismiss_delayed_filename(struct delayed_filename *);
 int putname_to_delayed(struct delayed_filename *, struct filename *);
 struct filename *complete_getname(struct delayed_filename *);
 
-static inline struct filename *refname(struct filename *name)
-{
-	atomic_inc(&name->refcnt);
-	return name;
-}
-
 extern int finish_open(struct file *file, struct dentry *dentry,
 			int (*open)(struct inode *, struct file *));
 extern int finish_no_open(struct file *file, struct dentry *dentry);
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 67d8da927381..b1dc9284550a 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -2169,6 +2169,12 @@ static struct audit_names *audit_alloc_name(struct audit_context *context,
 	return aname;
 }
 
+static inline struct filename *refname(struct filename *name)
+{
+	name->refcnt++;
+	return name;
+}
+
 /**
  * __audit_getname - add a name to the list
  * @name: name to add
-- 
2.47.3