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ucount: use atomic_long_try_cmpxchg() in atomic_long_inc_below()

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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: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Alexey 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uros Bizjak 2025-07-21 19:45:58 +02:00 committed by Andrew Morton
parent f8cd9193b6
commit 58b4fba81a
1 changed files with 6 additions and 8 deletions
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12
kernel/ucount.c
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@ -201,16 +201,14 @@ void put_ucounts(struct ucounts *ucounts)
static inline bool atomic_long_inc_below(atomic_long_t *v, long u) static inline bool atomic_long_inc_below(atomic_long_t *v, long u)
{ {
long c, old; long c = atomic_long_read(v);
c = atomic_long_read(v);
for (;;) { do {
if (unlikely(c >= u)) if (unlikely(c >= u))
return false; return false;
old = atomic_long_cmpxchg(v, c, c+1); } while (!atomic_long_try_cmpxchg(v, &c, c+1));
if (likely(old == c))
return true; return true;
c = old;
}
} }
struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,