[PATCH RESEND 1/2] ucount: Fix atomic_long_inc_below argument typei()

[PATCH RESEND 1/2] ucount: Fix atomic_long_inc_below argument typei()

[Uros Bizjak]

The type of u argument of atomic_long_inc_below() should be long
to avoid unwanted truncation to int.

Fixes: f9c82a4ea89c ("Increase size of ucounts to atomic_long_t")
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Alexey Gladkov <legion@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: MengEn Sun <mengensun@tencent.com>
Cc: "Thomas Weißschuh" <linux@weissschuh.net>
---
 kernel/ucount.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/ucount.c b/kernel/ucount.c
index 8686e329b8f2..f629db485a07 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -199,7 +199,7 @@ void put_ucounts(struct ucounts *ucounts)
 	}
 }
 
-static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
+static inline bool atomic_long_inc_below(atomic_long_t *v, long u)
 {
 	long c, old;
 	c = atomic_long_read(v);
-- 
2.50.1

[PATCH RESEND 2/2] ucount: Use atomic_long_try_cmpxchg() in atomic_long_inc_below()

[Uros Bizjak]

Use atomic_long_try_cmpxchgi() instead of
atomic_long_cmpxchg (*ptr, old, new) == old in atomic_long_inc_belowi().
x86 CMPXCHG instruction returns success in ZF flag, so this change saves
a compare after cmpxchg (and related move instruction in front of cmpxchg).

Also, atomic_long_try_cmpxchg implicitly assigns old *ptr value to "old"
when cmpxchg fails, enabling further code simplifications.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Alexey Gladkov <legion@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Alexey Gladkov <legion@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: MengEn Sun <mengensun@tencent.com>
Cc: "Thomas Weißschuh" <linux@weissschuh.net>
---
 kernel/ucount.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/kernel/ucount.c b/kernel/ucount.c
index f629db485a07..586af49fc03e 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -201,16 +201,14 @@ void put_ucounts(struct ucounts *ucounts)
 
 static inline bool atomic_long_inc_below(atomic_long_t *v, long u)
 {
-	long c, old;
-	c = atomic_long_read(v);
-	for (;;) {
+	long c = atomic_long_read(v);
+
+	do {
 		if (unlikely(c >= u))
 			return false;
-		old = atomic_long_cmpxchg(v, c, c+1);
-		if (likely(old == c))
-			return true;
-		c = old;
-	}
+	} while (!atomic_long_try_cmpxchg(v, &c, c+1));
+
+	return true;
 }
 
 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
-- 
2.50.1

Re: [PATCH RESEND 1/2] ucount: Fix atomic_long_inc_below argument typei()

[Uros Bizjak]

Sorry, patches in this series have some problems in their description,
please expect v2.

Uros.

On Mon, Jul 21, 2025 at 7:42 PM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> The type of u argument of atomic_long_inc_below() should be long
> to avoid unwanted truncation to int.
>
> Fixes: f9c82a4ea89c ("Increase size of ucounts to atomic_long_t")
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Alexey Gladkov <legion@kernel.org>
> Cc: Roman Gushchin <roman.gushchin@linux.dev>
> Cc: MengEn Sun <mengensun@tencent.com>
> Cc: "Thomas Weißschuh" <linux@weissschuh.net>
> ---
>  kernel/ucount.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 8686e329b8f2..f629db485a07 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -199,7 +199,7 @@ void put_ucounts(struct ucounts *ucounts)
>         }
>  }
>
> -static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
> +static inline bool atomic_long_inc_below(atomic_long_t *v, long u)
>  {
>         long c, old;
>         c = atomic_long_read(v);
> --
> 2.50.1
>