jump_label: Use atomic_try_cmpxchg() in static_key_slow_inc_cpuslocked()

[ Upstream commit d0c00640 ]

Use atomic_try_cmpxchg() instead of atomic_cmpxchg (*ptr, old, new) ==
old in static_key_slow_inc_cpuslocked().  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_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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20221019140850.3395-1-ubizjak@gmail.com


Stable-dep-of: 83ab38ef ("jump_label: Fix concurrency issues in static_key_slow_dec()")
Signed-off-by: Sasha Levin <sashal@kernel.org>