kernel: support dynamic thread stack allocation

include/zephyr/kernel.h

@@ -265,6 +265,35 @@ extern void k_thread_foreach_unlocked(
 /* end - thread options */
 
 #if !defined(_ASMLANGUAGE)
+/**
+ * @brief Dynamically allocate a thread stack.
+ *
+ * Relevant stack creation flags include:
+ * - @ref K_USER allocate a userspace thread (requires `CONFIG_USERSPACE=y`)
+ *
+ * @param size Stack size in bytes.
+ * @param flags Stack creation flags, or 0.
+ *
+ * @retval the allocated thread stack on success.
+ * @retval NULL on failure.
+ *
+ * @see CONFIG_DYNAMIC_THREAD
+ */
+__syscall k_thread_stack_t *k_thread_stack_alloc(size_t size, int flags);
+
+/**
+ * @brief Free a dynamically allocated thread stack.
+ *
+ * @param stack Pointer to the thread stack.
+ *
+ * @retval 0 on success.
+ * @retval -EBUSY if the thread stack is in use.
+ * @retval -EINVAL if @p stack is invalid.
+ *
+ * @see CONFIG_DYNAMIC_THREAD
+ */
+__syscall int k_thread_stack_free(k_thread_stack_t *stack);
+
 /**
  * @brief Create a thread.
  *

kernel/CMakeLists.txt

@@ -122,6 +122,12 @@ target_sources_ifdef(
   userspace.c
   )
 
+target_sources_ifdef(
+  CONFIG_DYNAMIC_THREAD
+  kernel PRIVATE
+  dynamic.c
+  )
+
 target_include_directories(kernel PRIVATE
   ${ZEPHYR_BASE}/kernel/include
   ${ARCH_DIR}/${ARCH}/include

kernel/Kconfig

@@ -203,6 +203,68 @@ config THREAD_USERSPACE_LOCAL_DATA
 	depends on USERSPACE
 	default y if ERRNO && !ERRNO_IN_TLS
 
+config DYNAMIC_THREAD
+	bool "Support for dynamic threads [EXPERIMENTAL]"
+	select EXPERIMENTAL
+	depends on THREAD_STACK_INFO
+	select DYNAMIC_OBJECTS if USERSPACE
+	help
+	  Enable support for dynamic threads and stacks.
+
+if DYNAMIC_THREAD
+
+config DYNAMIC_THREAD_STACK_SIZE
+	int "Size of each pre-allocated thread stack"
+	default 1024 if !64BIT
+	default 2048 if 64BIT
+	help
+	  Default stack size (in bytes) for dynamic threads.
+
+config DYNAMIC_THREAD_ALLOC
+	bool "Support heap-allocated thread objects and stacks"
+	help
+	  Select this option to enable allocating thread object and
+	  thread stacks from the system heap.
+
+	  Only use this type of allocation in situations
+	  where malloc is permitted.
+
+config DYNAMIC_THREAD_POOL_SIZE
+	int "Number of statically pre-allocated threads"
+	default 0
+	range 0 8192
+	help
+	  Pre-allocate a fixed number of thread objects and
+	  stacks at build time.
+
+	  This type of "dynamic" stack is usually suitable in
+	  situations where malloc is not permitted.
+
+choice DYNAMIC_THREAD_PREFER
+	prompt "Preferred dynamic thread allocator"
+	default DYNAMIC_THREAD_PREFER_POOL
+	help
+	  If both CONFIG_DYNAMIC_THREAD_ALLOC=y and
+	  CONFIG_DYNAMIC_THREAD_POOL_SIZE > 0, then the user may
+	  specify the order in which allocation is attmpted.
+
+config DYNAMIC_THREAD_PREFER_ALLOC
+	bool "Prefer heap-based allocation"
+	depends on DYNAMIC_THREAD_ALLOC
+	help
+	  Select this option to attempt a heap-based allocation
+	  prior to any pool-based allocation.
+
+config DYNAMIC_THREAD_PREFER_POOL
+	bool "Prefer pool-based allocation"
+	help
+	  Select this option to attempt a pool-based allocation
+	  prior to any heap-based allocation.
+
+endchoice # DYNAMIC_THREAD_PREFER
+
+endif # DYNAMIC_THREADS
+
 config LIBC_ERRNO
 	bool
 	help

kernel/dynamic.c

@@ -0,0 +1,162 @@
+/*
+ * Copyright (c) 2022, Meta
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "kernel_internal.h"
+
+#include <zephyr/kernel.h>
+#include <zephyr/kernel/thread_stack.h>
+#include <zephyr/logging/log.h>
+#include <zephyr/sys/bitarray.h>
+
+LOG_MODULE_DECLARE(os, CONFIG_KERNEL_LOG_LEVEL);
+
+#if CONFIG_DYNAMIC_THREAD_POOL_SIZE > 0
+#define BA_SIZE CONFIG_DYNAMIC_THREAD_POOL_SIZE
+#else
+#define BA_SIZE 1
+#endif
+
+struct dyn_cb_data {
+	k_tid_t tid;
+	k_thread_stack_t *stack;
+};
+
+static K_THREAD_STACK_ARRAY_DEFINE(dynamic_stack, CONFIG_DYNAMIC_THREAD_POOL_SIZE,
+				   CONFIG_DYNAMIC_THREAD_STACK_SIZE);
+SYS_BITARRAY_DEFINE_STATIC(dynamic_ba, BA_SIZE);
+
+static k_thread_stack_t *z_thread_stack_alloc_dyn(size_t align, size_t size)
+{
+	return z_thread_aligned_alloc(align, size);
+}
+
+static k_thread_stack_t *z_thread_stack_alloc_pool(size_t size)
+{
+	int rv;
+	size_t offset;
+	k_thread_stack_t *stack;
+
+	if (size > CONFIG_DYNAMIC_THREAD_STACK_SIZE) {
+		LOG_DBG("stack size %zu is > pool stack size %d", size,
+			CONFIG_DYNAMIC_THREAD_STACK_SIZE);
+		return NULL;
+	}
+
+	rv = sys_bitarray_alloc(&dynamic_ba, 1, &offset);
+	if (rv < 0) {
+		LOG_DBG("unable to allocate stack from pool");
+		return NULL;
+	}
+
+	__ASSERT_NO_MSG(offset < CONFIG_DYNAMIC_THREAD_POOL_SIZE);
+
+	stack = (k_thread_stack_t *)&dynamic_stack[offset];
+
+	return stack;
+}
+
+k_thread_stack_t *z_impl_k_thread_stack_alloc(size_t size, int flags)
+{
+	size_t align = 0;
+	size_t obj_size = 0;
+	k_thread_stack_t *stack = NULL;
+
+#ifdef CONFIG_USERSPACE
+	if ((flags & K_USER) != 0) {
+		align = Z_THREAD_STACK_OBJ_ALIGN(size);
+		obj_size = Z_THREAD_STACK_SIZE_ADJUST(size);
+	} else
+#endif
+	{
+		align = Z_KERNEL_STACK_OBJ_ALIGN;
+		obj_size = Z_KERNEL_STACK_SIZE_ADJUST(size);
+	}
+
+	if (IS_ENABLED(CONFIG_DYNAMIC_THREAD_PREFER_ALLOC)) {
+		stack = z_thread_stack_alloc_dyn(align, obj_size);
+		if (stack == NULL && CONFIG_DYNAMIC_THREAD_POOL_SIZE > 0) {
+			stack = z_thread_stack_alloc_pool(size);
+		}
+	} else if (IS_ENABLED(CONFIG_DYNAMIC_THREAD_PREFER_POOL) &&
+		   CONFIG_DYNAMIC_THREAD_POOL_SIZE > 0) {
+		stack = z_thread_stack_alloc_pool(size);
+		if (stack == NULL && IS_ENABLED(CONFIG_DYNAMIC_THREAD_ALLOC)) {
+			stack = z_thread_stack_alloc_dyn(align, obj_size);
+		}
+	} else {
+		return NULL;
+	}
+
+	return stack;
+}
+
+#ifdef CONFIG_USERSPACE
+static inline k_thread_stack_t *z_vrfy_k_thread_stack_alloc(size_t size, int flags)
+{
+	return z_impl_k_thread_stack_alloc(size, flags);
+}
+#include <syscalls/k_thread_stack_alloc_mrsh.c>
+#endif
+
+static void dyn_cb(const struct k_thread *thread, void *user_data)
+{
+	struct dyn_cb_data *const data = (struct dyn_cb_data *)user_data;
+
+	if (data->stack == (k_thread_stack_t *)thread->stack_info.start) {
+		__ASSERT(data->tid == NULL, "stack %p is associated with more than one thread!");
+		data->tid = (k_tid_t)thread;
+	}
+}
+
+int z_impl_k_thread_stack_free(k_thread_stack_t *stack)
+{
+	char state_buf[16] = {0};
+	struct dyn_cb_data data = {.stack = stack};
+
+	/* Get a possible tid associated with stack */
+	k_thread_foreach(dyn_cb, &data);
+
+	if (data.tid != NULL) {
+		/* Check if thread is in use */
+		if (k_thread_state_str(data.tid, state_buf, sizeof(state_buf)) != state_buf) {
+			LOG_ERR("tid %p is invalid!", data.tid);
+			return -EINVAL;
+		}
+
+		if (!(strcmp("dummy", state_buf) == 0) || (strcmp("dead", state_buf) == 0)) {
+			LOG_ERR("tid %p is in use!", data.tid);
+			return -EBUSY;
+		}
+	}
+
+	if (CONFIG_DYNAMIC_THREAD_POOL_SIZE > 0) {
+		if (IS_ARRAY_ELEMENT(dynamic_stack, stack)) {
+			if (sys_bitarray_free(&dynamic_ba, 1, ARRAY_INDEX(dynamic_stack, stack))) {
+				LOG_ERR("stack %p is not allocated!", stack);
+				return -EINVAL;
+			}
+
+			return 0;
+		}
+	}
+
+	if (IS_ENABLED(CONFIG_DYNAMIC_THREAD_ALLOC)) {
+		k_free(stack);
+	} else {
+		LOG_ERR("Invalid stack %p", stack);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+#ifdef CONFIG_USERSPACE
+static inline int z_vrfy_k_thread_stack_free(k_thread_stack_t *stack)
+{
+	return z_impl_k_thread_stack_free(stack);
+}
+#include <syscalls/k_thread_stack_free_mrsh.c>
+#endif

tests/kernel/threads/dynamic_thread_stack/CMakeLists.txt

@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+find_package(Zephyr HINTS $ENV{ZEPHYR_BASE})
+project(dynamic_thread_stack)
+
+FILE(GLOB app_sources src/*.c)
+target_sources(app PRIVATE ${app_sources})

tests/kernel/threads/dynamic_thread_stack/prj.conf

@@ -0,0 +1,14 @@
+CONFIG_ZTEST=y
+CONFIG_ZTEST_NEW_API=y
+CONFIG_INIT_STACKS=y
+CONFIG_THREAD_STACK_INFO=y
+CONFIG_MAX_THREAD_BYTES=5
+CONFIG_DYNAMIC_THREAD=y
+CONFIG_DYNAMIC_THREAD_POOL_SIZE=2
+CONFIG_DYNAMIC_THREAD_ALLOC=y
+CONFIG_HEAP_MEM_POOL_SIZE=16384
+CONFIG_ZTEST_STACK_SIZE=2048
+CONFIG_MAIN_STACK_SIZE=2048
+
+CONFIG_HW_STACK_PROTECTION=n
+CONFIG_TEST_HW_STACK_PROTECTION=n