The patch titled
Subject: ucount: Use rcuref_t for reference counting
has been added to the -mm mm-nonmm-unstable branch. Its filename is
ucount-use-rcuref_t-for-reference-counting.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/ucount-use-rcuref_t-for-reference-counting.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Acked-by:Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Lai jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Mengen Sun <mengensun@xxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: "Uladzislau Rezki (Sony)" <urezki@xxxxxxxxx>
Cc: YueHong Wu <yuehongwu@xxxxxxxxxxx>
Cc: Zqiang <qiang.zhang1211@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxxxxx are
rcu-provide-a-static-initializer-for-hlist_nulls_head.patch
ucount-replace-get_ucounts_or_wrap-with-atomic_inc_not_zero.patch
ucount-use-rcu-for-ucounts-lookups.patch
ucount-use-rcuref_t-for-reference-counting.patch
