diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2025-07-21 19:45:58 +0200 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-08-02 12:01:38 -0700 |
| commit | 58b4fba81a2e400a47ddbe7c1dc0a2bc038313b7 (patch) | |
| tree | 6f8e874cbcb17856c60ab3a60ae8b9151a279248 | |
| parent | f8cd9193b62e92ad25def5370ca8ea2bc7585381 (diff) | |
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: 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>
| -rw-r--r-- | kernel/ucount.c | 14 |
1 files 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, |