kernek: don't allow mutex ops in ISRs

Mutex operations check ownership against _current. But in an
ISR, _current is just whatever thread was interrupted when the
ISR fired. Explicitly do not allow this.

Signed-off-by: Andrew Boie <[email protected]>

include/kernel.h

@@ -3610,6 +3610,8 @@ __syscall int k_mutex_init(struct k_mutex *mutex);
  * A thread is permitted to lock a mutex it has already locked. The operation
  * completes immediately and the lock count is increased by 1.
  *
+ * Mutexes may not be locked in ISRs.
+ *
  * @param mutex Address of the mutex.
  * @param timeout Waiting period to lock the mutex,
  *                or one of the special values K_NO_WAIT and
@@ -3631,6 +3633,9 @@ __syscall int k_mutex_lock(struct k_mutex *mutex, k_timeout_t timeout);
  * the calling thread as many times as it was previously locked by that
  * thread.
  *
+ * Mutexes may not be unlocked in ISRs, as mutexes must only be manipulated
+ * in thread context due to ownership and priority inheritance semantics.
+ *
  * @param mutex Address of the mutex.
  *
  * @retval 0 Mutex unlocked.

kernel/mutex.c

@@ -122,6 +122,8 @@ int z_impl_k_mutex_lock(struct k_mutex *mutex, k_timeout_t timeout)
 	k_spinlock_key_t key;
 	bool resched = false;
 
+	__ASSERT(!arch_is_in_isr(), "mutexes cannot be used inside ISRs");
+
 	sys_trace_void(SYS_TRACE_ID_MUTEX_LOCK);
 	key = k_spin_lock(&lock);
 
@@ -211,6 +213,8 @@ int z_impl_k_mutex_unlock(struct k_mutex *mutex)
 {
 	struct k_thread *new_owner;
 
+	__ASSERT(!arch_is_in_isr(), "mutexes cannot be used inside ISRs");
+
 	CHECKIF(mutex->owner == NULL) {
 		return -EINVAL;
 	}