Use our own critical-section impl compatible with Rust 1.59

.github/.cspell/project-dictionary.txt

@@ -39,6 +39,7 @@ opensbi
 prefetcher
 quadword
 rclass
+reentrancy
 semihosting
 seqlock
 sifive

.github/.cspell/rust-dependencies.txt

@@ -3,10 +3,12 @@
 
 assertions
 atomic
+cell
 criterion
 critical
 crossbeam
 fastrand
+once
 paste
 portable
 quickcheck

Cargo.toml

@@ -62,9 +62,10 @@ serde = { version = "1.0.103", optional = true, default-features = false }
 critical-section = { version = "1", optional = true }
 
 [dev-dependencies]
-critical-section = { version = "1", features = ["std"] }
+critical-section = { version = "1", features = ["restore-state-bool"] }
 crossbeam-utils = "0.8"
 fastrand = "1"
+once_cell = "1"
 paste = "1"
 quickcheck = { default-features = false, git = "https://github.com/taiki-e/quickcheck.git", branch = "dev" } # https://github.com/BurntSushi/quickcheck/pull/304 + https://github.com/BurntSushi/quickcheck/pull/282 + lower MSRV
 serde = { version = "1", features = ["derive"] }

src/tests/critical_section_std.rs

@@ -0,0 +1,68 @@
+// Based on https://github.com/rust-embedded/critical-section/blob/v1.1.1/src/std.rs,
+// but compatible with Rust 1.59 that we run test.
+
+use std::{
+    cell::Cell,
+    mem::MaybeUninit,
+    sync::{Mutex, MutexGuard},
+};
+
+use once_cell::sync::Lazy;
+
+static GLOBAL_MUTEX: Lazy<Mutex<()>> = Lazy::new(|| Mutex::new(()));
+
+// This is initialized if a thread has acquired the CS, uninitialized otherwise.
+static mut GLOBAL_GUARD: MaybeUninit<MutexGuard<'static, ()>> = MaybeUninit::uninit();
+
+std::thread_local!(static IS_LOCKED: Cell<bool> = Cell::new(false));
+
+struct StdCriticalSection;
+critical_section::set_impl!(StdCriticalSection);
+
+unsafe impl critical_section::Impl for StdCriticalSection {
+    unsafe fn acquire() -> bool {
+        // Allow reentrancy by checking thread local state
+        IS_LOCKED.with(|l| {
+            if l.get() {
+                // CS already acquired in the current thread.
+                return true;
+            }
+
+            // Note: it is fine to set this flag *before* acquiring the mutex because it's thread local.
+            // No other thread can see its value, there's no potential for races.
+            // This way, we hold the mutex for slightly less time.
+            l.set(true);
+
+            // Not acquired in the current thread, acquire it.
+            let guard = match GLOBAL_MUTEX.lock() {
+                Ok(guard) => guard,
+                Err(err) => {
+                    // Ignore poison on the global mutex in case a panic occurred
+                    // while the mutex was held.
+                    err.into_inner()
+                }
+            };
+            unsafe {
+                GLOBAL_GUARD.write(guard);
+            }
+
+            false
+        })
+    }
+
+    unsafe fn release(nested_cs: bool) {
+        if !nested_cs {
+            // SAFETY: As per the acquire/release safety contract, release can only be called
+            // if the critical section is acquired in the current thread,
+            // in which case we know the GLOBAL_GUARD is initialized.
+            unsafe {
+                GLOBAL_GUARD.as_mut_ptr().drop_in_place();
+            }
+
+            // Note: it is fine to clear this flag *after* releasing the mutex because it's thread local.
+            // No other thread can see its value, there's no potential for races.
+            // This way, we hold the mutex for slightly less time.
+            IS_LOCKED.with(|l| l.set(false));
+        }
+    }
+}

src/tests/mod.rs

@@ -9,6 +9,8 @@
 #[macro_use]
 pub(crate) mod helper;
 
+#[cfg(feature = "critical-section")]
+mod critical_section_std;
 #[cfg(feature = "serde")]
 mod serde;