Commit 58b4fba8 authored by Uros Bizjak's avatar Uros Bizjak Committed by Andrew Morton
Browse files

ucount: use atomic_long_try_cmpxchg() in atomic_long_inc_below() 

Use atomic_long_try_cmpxchg() instead of
atomic_long_cmpxchg (*ptr, old, new) == old in atomic_long_inc_below().
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.

Link: https://lkml.kernel.org/r/20250721174610.28361-2-ubizjak@gmail.com


Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Reviewed-by: default avatarAlexey Gladkov <legion@kernel.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>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent f8cd9193

kernel/ucount.c

+6 −8
Original line number Diff line number Diff line
@@ -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))

	} while (!atomic_long_try_cmpxchg(v, &c, c+1));



	return true;

		c = old;

	}

}



struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,