linux-kernel - [PATCH v4 20/59] struct filename ->refcnt doesn't need to be atomic

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Message-ID: <20260108073803.425343-21-viro@zeniv.linux.org.uk>
Date: Thu,  8 Jan 2026 07:37:24 +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: [PATCH v4 20/59] 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         | 12 ++++++------
 include/linux/fs.h |  8 +-------
 kernel/auditsc.c   |  6 +++---
 3 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 4de9697bfbee..8f26e91de906 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)
@@ -292,13 +292,13 @@ 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))
@@ -328,12 +328,12 @@ int delayed_getname_uflags(struct delayed_filename *v, const char __user *string
 
 int putname_to_delayed(struct delayed_filename *v, struct filename *name)
 {
-	if (likely(atomic_read(&name->refcnt) == 1)) {
+	if (likely(name->refcnt == 1)) {
 		v->__incomplete_filename = name;
 		return 0;
 	}
+	name->refcnt--;
 	v->__incomplete_filename = do_getname_kernel(name->name, true);
-	putname(name);
 	return PTR_ERR_OR_ZERO(v->__incomplete_filename);
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9fe91db9c053..6aaaf57e90d8 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;
-}
-
 DEFINE_CLASS(filename, struct filename *, putname(_T), getname(p), const char __user *p)
 EXTEND_CLASS(filename, _kernel, getname_kernel(p), const char *p)
 EXTEND_CLASS(filename, _flags, getname_flags(p, f), const char __user *p, unsigned int f)
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 67d8da927381..86a44b162a87 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -2191,7 +2191,7 @@ void __audit_getname(struct filename *name)
 	n->name = name;
 	n->name_len = AUDIT_NAME_FULL;
 	name->aname = n;
-	refname(name);
+	name->refcnt++;
 }
 
 static inline int audit_copy_fcaps(struct audit_names *name,
@@ -2323,7 +2323,7 @@ void __audit_inode(struct filename *name, const struct dentry *dentry,
 		return;
 	if (name) {
 		n->name = name;
-		refname(name);
+		name->refcnt++;
 	}
 
 out:
@@ -2445,7 +2445,7 @@ void __audit_inode_child(struct inode *parent,
 		if (found_parent) {
 			found_child->name = found_parent->name;
 			found_child->name_len = AUDIT_NAME_FULL;
-			refname(found_child->name);
+			found_child->name->refcnt++;
 		}
 	}
 
-- 
2.47.3