Merge pull request #3573 from bugadani/enqueue

Unconditionally set `RUN_QUEUED`

4 files changed, 10 insertions, 38 deletions

diff --git a/embassy-executor/src/raw/mod.rs b/embassy-executor/src/raw/mod.rs
index 0ac569946..6503b556f 100644
--- a/embassy-executor/src/raw/mod.rs
+++ b/embassy-executor/src/raw/mod.rs
@@ -52,7 +52,7 @@ use super::SpawnToken;
 /// ```text
 ///    ┌────────────┐   ┌────────────────────────┐
 /// ┌─►│Not spawned │◄─6┤Not spawned|Run enqueued│
-/// │  │            ��   │                        │
+/// │  │            ��7��►��                        │
 /// │  └─────┬──────┘   └──────▲─────────────────┘
 /// │        1                 │
 /// │        │    ┌────────────┘
@@ -76,6 +76,7 @@ use super::SpawnToken;
 /// - 4: Task exits - `TaskStorage::poll -> Poll::Ready`
 /// - 5: A run-queued task exits - `TaskStorage::poll -> Poll::Ready`
 /// - 6: Task is dequeued and then ignored via `State::run_dequeue`
+/// - 7: A task is waken when it is not spawned - `wake_task -> State::run_enqueue`
 pub(crate) struct TaskHeader {
     pub(crate) state: State,
     pub(crate) run_queue_item: RunQueueItem,
diff --git a/embassy-executor/src/raw/state_atomics.rs b/embassy-executor/src/raw/state_atomics.rs
index 6f5266bda..bdd317b53 100644
--- a/embassy-executor/src/raw/state_atomics.rs
+++ b/embassy-executor/src/raw/state_atomics.rs
@@ -44,19 +44,8 @@ impl State {
     /// function if the task was successfully marked.
     #[inline(always)]
     pub fn run_enqueue(&self, f: impl FnOnce(Token)) {
-        if self
-            .state
-            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |state| {
-                // If already scheduled, or if not started,
-                if (state & STATE_RUN_QUEUED != 0) || (state & STATE_SPAWNED == 0) {
-                    None
-                } else {
-                    // Mark it as scheduled
-                    Some(state | STATE_RUN_QUEUED)
-                }
-            })
-            .is_ok()
-        {
+        let prev = self.state.fetch_or(STATE_RUN_QUEUED, Ordering::AcqRel);
+        if prev & STATE_RUN_QUEUED == 0 {
             locked(f);
         }
     }
diff --git a/embassy-executor/src/raw/state_atomics_arm.rs b/embassy-executor/src/raw/state_atomics_arm.rs
index 4896b33c5..cbda0d89d 100644
--- a/embassy-executor/src/raw/state_atomics_arm.rs
+++ b/embassy-executor/src/raw/state_atomics_arm.rs
@@ -1,4 +1,3 @@
-use core::arch::asm;
 use core::sync::atomic::{compiler_fence, AtomicBool, AtomicU32, Ordering};
 
 #[derive(Clone, Copy)]
@@ -67,24 +66,10 @@ impl State {
     /// function if the task was successfully marked.
     #[inline(always)]
     pub fn run_enqueue(&self, f: impl FnOnce(Token)) {
-        unsafe {
-            loop {
-                let state: u32;
-                asm!("ldrex {}, [{}]", out(reg) state, in(reg) self, options(nostack));
+        let old = self.run_queued.swap(true, Ordering::AcqRel);
 
-                if (state & STATE_RUN_QUEUED != 0) || (state & STATE_SPAWNED == 0) {
-                    asm!("clrex", options(nomem, nostack));
-                    return;
-                }
-
-                let outcome: usize;
-                let new_state = state | STATE_RUN_QUEUED;
-                asm!("strex {}, {}, [{}]", out(reg) outcome, in(reg) new_state, in(reg) self, options(nostack));
-                if outcome == 0 {
-                    locked(f);
-                    return;
-                }
-            }
+        if !old {
+            locked(f);
         }
     }
 
diff --git a/embassy-executor/src/raw/state_critical_section.rs b/embassy-executor/src/raw/state_critical_section.rs
index 29b10f6e3..4733af278 100644
--- a/embassy-executor/src/raw/state_critical_section.rs
+++ b/embassy-executor/src/raw/state_critical_section.rs
@@ -56,12 +56,9 @@ impl State {
     pub fn run_enqueue(&self, f: impl FnOnce(Token)) {
         critical_section::with(|cs| {
             if self.update_with_cs(cs, |s| {
-                if (*s & STATE_RUN_QUEUED != 0) || (*s & STATE_SPAWNED == 0) {
-                    false
-                } else {
-                    *s |= STATE_RUN_QUEUED;
-                    true
-                }
+                let ok = *s & STATE_RUN_QUEUED == 0;
+                *s |= STATE_RUN_QUEUED;
+                ok
             }) {
                 f(cs);
             }