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| author | Uros Bizjak <ubizjak@gmail.com> | 2022-10-17 16:40:49 +0200 |
|---|---|---|
| committer | Eric W. Biederman <ebiederm@xmission.com> | 2022-11-30 12:46:04 -0600 |
| commit | b4b11b58cd022df173f2df65633c9c583ade8a65 (patch) | |
| tree | 9d6c8c43b2d255919d6d9ba85312a78e27910704 | |
| parent | 295227b101925be9a407820b9be9e08c1b87df3d (diff) | |
| download | user-namespace-fix-atomic_lock_inc_below-for-v6.2.tar.gz | |
ucount: Use atomic_long_try_cmpxchg in atomic_long_inc_belowfix-atomic_lock_inc_below-for-v6.2
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>
Reviewed-by: Alexey Gladkov <legion@kernel.org>
Link: https://lkml.kernel.org/r/20221017144049.3404-3-ubizjak@gmail.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
| -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 74f5b4959febaf..2c04589a61ff79 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -214,16 +214,14 @@ 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, |