[merged mm-nonmm-stable] ucount-use-rcuref_t-for-reference-counting.patch removed from -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The quilt patch titled
     Subject: ucount: use rcuref_t for reference counting
has been removed from the -mm tree.  Its filename was
     ucount-use-rcuref_t-for-reference-counting.patch

This patch was dropped because it was merged into the mm-nonmm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: ucount: use rcuref_t for reference counting
Date: Mon, 3 Feb 2025 16:05:25 +0100

Use rcuref_t for reference counting.  This eliminates the cmpxchg loop in
the get and put path.  This also eliminates the need to acquire the lock
in the put path because once the final user returns the reference, it can
no longer be obtained anymore.

Use rcuref_t for reference counting.

Link: https://lkml.kernel.org/r/20250203150525.456525-5-bigeasy@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai jiangshan <jiangshanlai@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Mengen Sun <mengensun@tencent.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Cc: YueHong Wu <yuehongwu@tencent.com>
Cc: Zqiang <qiang.zhang1211@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/user_namespace.h |   11 +++++++++--
 kernel/ucount.c                |   16 +++++-----------
 2 files changed, 14 insertions(+), 13 deletions(-)

--- a/include/linux/user_namespace.h~ucount-use-rcuref_t-for-reference-counting
+++ a/include/linux/user_namespace.h
@@ -8,6 +8,7 @@
 #include <linux/rculist_nulls.h>
 #include <linux/sched.h>
 #include <linux/workqueue.h>
+#include <linux/rcuref.h>
 #include <linux/rwsem.h>
 #include <linux/sysctl.h>
 #include <linux/err.h>
@@ -120,7 +121,7 @@ struct ucounts {
 	struct user_namespace *ns;
 	kuid_t uid;
 	struct rcu_head rcu;
-	atomic_t count;
+	rcuref_t count;
 	atomic_long_t ucount[UCOUNT_COUNTS];
 	atomic_long_t rlimit[UCOUNT_RLIMIT_COUNTS];
 };
@@ -133,9 +134,15 @@ void retire_userns_sysctls(struct user_n
 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type);
 void dec_ucount(struct ucounts *ucounts, enum ucount_type type);
 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
-struct ucounts * __must_check get_ucounts(struct ucounts *ucounts);
 void put_ucounts(struct ucounts *ucounts);
 
+static inline struct ucounts * __must_check get_ucounts(struct ucounts *ucounts)
+{
+	if (rcuref_get(&ucounts->count))
+		return ucounts;
+	return NULL;
+}
+
 static inline long get_rlimit_value(struct ucounts *ucounts, enum rlimit_type type)
 {
 	return atomic_long_read(&ucounts->rlimit[type]);
--- a/kernel/ucount.c~ucount-use-rcuref_t-for-reference-counting
+++ a/kernel/ucount.c
@@ -11,7 +11,7 @@
 struct ucounts init_ucounts = {
 	.ns    = &init_user_ns,
 	.uid   = GLOBAL_ROOT_UID,
-	.count = ATOMIC_INIT(1),
+	.count = RCUREF_INIT(1),
 };
 
 #define UCOUNTS_HASHTABLE_BITS 10
@@ -138,7 +138,7 @@ static struct ucounts *find_ucounts(stru
 	guard(rcu)();
 	hlist_nulls_for_each_entry_rcu(ucounts, pos, hashent, node) {
 		if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns)) {
-			if (atomic_inc_not_zero(&ucounts->count))
+			if (rcuref_get(&ucounts->count))
 				return ucounts;
 		}
 	}
@@ -154,13 +154,6 @@ static void hlist_add_ucounts(struct uco
 	spin_unlock_irq(&ucounts_lock);
 }
 
-struct ucounts *get_ucounts(struct ucounts *ucounts)
-{
-	if (atomic_inc_not_zero(&ucounts->count))
-		return ucounts;
-	return NULL;
-}
-
 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 {
 	struct hlist_nulls_head *hashent = ucounts_hashentry(ns, uid);
@@ -176,7 +169,7 @@ struct ucounts *alloc_ucounts(struct use
 
 	new->ns = ns;
 	new->uid = uid;
-	atomic_set(&new->count, 1);
+	rcuref_init(&new->count, 1);
 
 	spin_lock_irq(&ucounts_lock);
 	ucounts = find_ucounts(ns, uid, hashent);
@@ -196,7 +189,8 @@ void put_ucounts(struct ucounts *ucounts
 {
 	unsigned long flags;
 
-	if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) {
+	if (rcuref_put(&ucounts->count)) {
+		spin_lock_irqsave(&ucounts_lock, flags);
 		hlist_nulls_del_rcu(&ucounts->node);
 		spin_unlock_irqrestore(&ucounts_lock, flags);
 
_

Patches currently in -mm which might be from bigeasy@linutronix.de are