fork, IA64: Provide alloc_thread_stack_node() for IA64

Provide a generic alloc_thread_stack_node() for IA64 and
CONFIG_ARCH_THREAD_STACK_ALLOCATOR which returns stack pointer and sets
task_struct::stack so it behaves exactly like the other implementations.

Rename IA64's alloc_thread_stack_node() and add the generic version to the
fork code so it is in one place _and_ to drastically lower the chances of
fat fingering the IA64 code.  Do the same for free_thread_stack().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20220217102406.3697941-4-bigeasy@linutronix.de

Author: Sebastian Andrzej Siewior

arch/ia64/include/asm/thread_info.h

@@ -55,15 +55,15 @@ struct thread_info {
 #ifndef ASM_OFFSETS_C
 /* how to get the thread information struct from C */
 #define current_thread_info()	((struct thread_info *) ((char *) current + IA64_TASK_SIZE))
-#define alloc_thread_stack_node(tsk, node)	\
+#define arch_alloc_thread_stack_node(tsk, node)	\
 		((unsigned long *) ((char *) (tsk) + IA64_TASK_SIZE))
 #define task_thread_info(tsk)	((struct thread_info *) ((char *) (tsk) + IA64_TASK_SIZE))
 #else
 #define current_thread_info()	((struct thread_info *) 0)
-#define alloc_thread_stack_node(tsk, node)	((unsigned long *) 0)
+#define arch_alloc_thread_stack_node(tsk, node)	((unsigned long *) 0)
 #define task_thread_info(tsk)	((struct thread_info *) 0)
 #endif
-#define free_thread_stack(tsk)	/* nothing */
+#define arch_free_thread_stack(tsk)	/* nothing */
 #define task_stack_page(tsk)	((void *)(tsk))
 
 #define __HAVE_THREAD_FUNCTIONS

kernel/fork.c

@@ -330,6 +330,23 @@ void thread_stack_cache_init(void)
 }
 
 # endif /* THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK) */
+#else /* CONFIG_ARCH_THREAD_STACK_ALLOCATOR */
+
+static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
+{
+	unsigned long *stack;
+
+	stack = arch_alloc_thread_stack_node(tsk, node);
+	tsk->stack = stack;
+	return stack;
+}
+
+static void free_thread_stack(struct task_struct *tsk)
+{
+	arch_free_thread_stack(tsk);
+	tsk->stack = NULL;
+}
+
 #endif /* !CONFIG_ARCH_THREAD_STACK_ALLOCATOR */
 
 /* SLAB cache for signal_struct structures (tsk->signal) */