Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH 2/2] ucount: Use atomic_long_try_cmpxchg in atomic_long_inc_below | Date | Wed, 13 Jul 2022 17:54:05 +0200 |
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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.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> --- kernel/ucount.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/kernel/ucount.c b/kernel/ucount.c index 974ac1585009..5d980460104e 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -218,16 +218,14 @@ 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, -- 2.35.3
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