From 7d4defa5e52a035e49c78f4958392cdb4d480c8b Mon Sep 17 00:00:00 2001
From: 4lDO2 <4lDO2@protonmail.com>
Date: Fri, 19 Mar 2021 11:07:41 +0100
Subject: [PATCH] Use weak CAS and use abort() in context::switch.

Previously context::switch used compare_and_swap for acquiring the
global context switch lock, but given its deprecation in more recent
Rust versions, it has been replaced with compare_exchange_weak (which
can be further optimized on some architectures).

It also replaces panic!() with abort() in switch_finish_hook, because
unwinding from assembly is not that fun.
---
 src/context/switch.rs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/context/switch.rs b/src/context/switch.rs
index 2c37430..a823854 100644
--- a/src/context/switch.rs
+++ b/src/context/switch.rs
@@ -78,7 +78,8 @@ pub unsafe extern "C" fn switch_finish_hook() {
         prev_lock.force_write_unlock();
         next_lock.force_write_unlock();
     } else {
-        panic!("SWITCH_RESULT was not set");
+        // TODO: unreachable_unchecked()?
+        core::intrinsics::abort();
     }
     arch::CONTEXT_SWITCH_LOCK.store(false, Ordering::SeqCst);
 }
@@ -97,11 +98,12 @@ unsafe fn runnable(context: &Context, cpu_id: usize) -> bool {
 ///
 /// Do not call this while holding locks!
 pub unsafe fn switch() -> bool {
+    // TODO: Better memory orderings?
     //set PIT Interrupt counter to 0, giving each process same amount of PIT ticks
     let ticks = PIT_TICKS.swap(0, Ordering::SeqCst);
 
     // Set the global lock to avoid the unsafe operations below from causing issues
-    while arch::CONTEXT_SWITCH_LOCK.compare_and_swap(false, true, Ordering::SeqCst) {
+    while arch::CONTEXT_SWITCH_LOCK.compare_exchange_weak(false, true, Ordering::SeqCst, Ordering::Relaxed).is_err() {
         interrupt::pause();
     }