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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2025-02-03 16:05:25 +0100
committerAndrew Morton <akpm@linux-foundation.org>2025-03-16 22:30:50 -0700
commitb4dc0bee2a749083028afba346910e198653f42a (patch)
tree6cca8e505189d9fde61d736a4f8dd605891b40de
parent5f01a22c5b231dd590f61a2591b3090665733bcb (diff)
ucount: use rcuref_t for reference counting
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>
-rw-r--r--include/linux/user_namespace.h11
-rw-r--r--kernel/ucount.c16
2 files changed, 14 insertions, 13 deletions
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index ad4dbef92597..a0bb6d012137 100644
--- a/include/linux/user_namespace.h
+++ b/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_namespace *ns);
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]);
diff --git a/kernel/ucount.c b/kernel/ucount.c
index b6abaf68cdcc..8686e329b8f2 100644
--- a/kernel/ucount.c
+++ b/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(struct user_namespace *ns, kuid_t uid,
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 ucounts *ucounts)
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 user_namespace *ns, kuid_t uid)
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);