1 files changed, 21 insertions, 12 deletions

diff --git a/libcr_ipc/include/libcr_ipc/sema.h b/libcr_ipc/include/libcr_ipc/sema.h
index 1064182..6db4015 100644
--- a/libcr_ipc/include/libcr_ipc/sema.h
+++ b/libcr_ipc/include/libcr_ipc/sema.h
@@ -1,12 +1,14 @@
 /* libcr_ipc/sema.h - Simple semaphores for libcr
  *
- * Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
  */
 
 #ifndef _LIBCR_IPC_SEMA_H_
 #define _LIBCR_IPC_SEMA_H_
 
+#include <stdbool.h>
+
 #include <libcr/coroutine.h> /* for cid_t, cr_* */
 
 #include <libcr_ipc/_linkedlist.h>
@@ -23,6 +25,7 @@ struct _cr_sema_waiter {
  */
 typedef struct {
 	unsigned int            cnt;
+	bool                    unpausing;
 	_cr_ipc_sll_root        waiters;
 } cr_sema_t;
 
@@ -39,10 +42,10 @@ static inline void cr_sema_signal(cr_sema_t *sema) {
 
 	bool saved = cr_save_and_disable_interrupts();
 	sema->cnt++;
-	if (sema->waiters.front) {
+	if (sema->waiters.front && !sema->unpausing) {
 		cr_unpause(
 			_cr_ipc_sll_node_cast(struct _cr_sema_waiter, sema->waiters.front)->cid);
-		_cr_ipc_sll_pop_from_front(&sema->waiters);
+		sema->unpausing = true;
 	}
 	cr_restore_interrupts(saved);
 }
@@ -57,10 +60,10 @@ static inline void cr_sema_signal_from_intrhandler(cr_sema_t *sema)  {
 	cr_assert_in_intrhandler();
 
 	sema->cnt++;
-	if (sema->waiters.front) {
+	if (sema->waiters.front && !sema->unpausing) {
 		cr_unpause_from_intrhandler(
 			_cr_ipc_sll_node_cast(struct _cr_sema_waiter, sema->waiters.front)->cid);
-		_cr_ipc_sll_pop_from_front(&sema->waiters);
+		sema->unpausing = true;
 	}
 }
 
@@ -76,15 +79,21 @@ static inline void cr_sema_wait(cr_sema_t *sema) {
 	cr_assert_in_coroutine();
 
 	bool saved = cr_save_and_disable_interrupts();
-	if (!sema->cnt) {
-		struct _cr_sema_waiter self = {
-			.cid    = cr_getcid(),
-		};
-		_cr_ipc_sll_push_to_rear(&sema->waiters, &self);
+
+	struct _cr_sema_waiter self = {
+		.cid    = cr_getcid(),
+	};
+	_cr_ipc_sll_push_to_rear(&sema->waiters, &self);
+	if (sema->waiters.front != &self || !sema->cnt)
 		cr_pause_and_yield();
-	}
-	assert(sema->cnt);
+	assert(sema->waiters.front == &self && sema->cnt);
+	_cr_ipc_sll_pop_from_front(&sema->waiters);
 	sema->cnt--;
+	if (sema->cnt && sema->waiters.front)
+		cr_unpause(
+			_cr_ipc_sll_node_cast(struct _cr_sema_waiter, sema->waiters.front)->cid);
+	else
+		sema->unpausing = false;
 	cr_restore_interrupts(saved);
 }