posix: sched: ensure min and max priority are schedulable

Previously, there was an off-by-one error for SCHED_RR.

Fixes #56729

Signed-off-by: Chris Friedt <[email protected]>

Author: cfriedt

lib/posix/pthread.c

@@ -18,12 +18,10 @@
 #define PTHREAD_INIT_FLAGS	PTHREAD_CANCEL_ENABLE
 #define PTHREAD_CANCELED	((void *) -1)
 
-#define LOWEST_POSIX_THREAD_PRIORITY 1
-
 K_MUTEX_DEFINE(pthread_once_lock);
 
 static const struct pthread_attr init_pthread_attrs = {
-	.priority = LOWEST_POSIX_THREAD_PRIORITY,
+	.priority = 0,
 	.stack = NULL,
 	.stacksize = 0,
 	.flags = PTHREAD_INIT_FLAGS,
@@ -73,9 +71,11 @@ static uint32_t zephyr_to_posix_priority(int32_t z_prio, int *policy)
 	if (z_prio < 0) {
 		*policy = SCHED_FIFO;
 		prio = -1 * (z_prio + 1);
+		__ASSERT_NO_MSG(prio < CONFIG_NUM_COOP_PRIORITIES);
 	} else {
 		*policy = SCHED_RR;
-		prio = (CONFIG_NUM_PREEMPT_PRIORITIES - z_prio);
+		prio = (CONFIG_NUM_PREEMPT_PRIORITIES - z_prio - 1);
+		__ASSERT_NO_MSG(prio < CONFIG_NUM_PREEMPT_PRIORITIES);
 	}
 
 	return prio;
@@ -87,9 +87,11 @@ static int32_t posix_to_zephyr_priority(uint32_t priority, int policy)
 
 	if (policy == SCHED_FIFO) {
 		/* Zephyr COOP priority starts from -1 */
+		__ASSERT_NO_MSG(priority < CONFIG_NUM_COOP_PRIORITIES);
 		prio =  -1 * (priority + 1);
 	} else {
-		prio = (CONFIG_NUM_PREEMPT_PRIORITIES - priority);
+		__ASSERT_NO_MSG(priority < CONFIG_NUM_PREEMPT_PRIORITIES);
+		prio = (CONFIG_NUM_PREEMPT_PRIORITIES - priority - 1);
 	}
 
 	return prio;

lib/posix/pthread_sched.c

@@ -7,13 +7,9 @@
 #include <zephyr/kernel.h>
 #include <zephyr/posix/sched.h>
 
-static bool valid_posix_policy(int policy)
+static inline bool valid_posix_policy(int policy)
 {
-	if (policy != SCHED_FIFO && policy != SCHED_RR) {
-		return false;
-	}
-
-	return true;
+	return policy == SCHED_FIFO || policy == SCHED_RR;
 }
 
 /**
@@ -23,25 +19,12 @@ static bool valid_posix_policy(int policy)
  */
 int sched_get_priority_min(int policy)
 {
-	if (valid_posix_policy(policy) == false) {
+	if (!valid_posix_policy(policy)) {
 		errno = EINVAL;
 		return -1;
 	}
 
-	if (IS_ENABLED(CONFIG_COOP_ENABLED)) {
-		if (policy == SCHED_FIFO) {
-			return 0;
-		}
-	}
-
-	if (IS_ENABLED(CONFIG_PREEMPT_ENABLED)) {
-		if (policy == SCHED_RR) {
-			return 0;
-		}
-	}
-
-	errno = EINVAL;
-	return -1;
+	return 0;
 }
 
 /**
@@ -51,25 +34,10 @@ int sched_get_priority_min(int policy)
  */
 int sched_get_priority_max(int policy)
 {
-	if (valid_posix_policy(policy) == false) {
-		errno = EINVAL;
-		return -1;
-	}
-
-	if (IS_ENABLED(CONFIG_COOP_ENABLED)) {
-		if (policy == SCHED_FIFO) {
-			/* Posix COOP priority starts from 0
-			 * whereas zephyr starts from -1
-			 */
-			return (CONFIG_NUM_COOP_PRIORITIES - 1);
-		}
-
-	}
-
-	if (IS_ENABLED(CONFIG_PREEMPT_ENABLED)) {
-		if (policy == SCHED_RR) {
-			return CONFIG_NUM_PREEMPT_PRIORITIES;
-		}
+	if (IS_ENABLED(CONFIG_COOP_ENABLED) && policy == SCHED_FIFO) {
+		return CONFIG_NUM_COOP_PRIORITIES - 1;
+	} else if (IS_ENABLED(CONFIG_PREEMPT_ENABLED) && policy == SCHED_RR) {
+		return CONFIG_NUM_PREEMPT_PRIORITIES - 1;
 	}
 
 	errno = EINVAL;