arch: remove ARCH_TASK_STRUCT_ALLOCATOR

IA-64 was the only architecture which selected ARCH_TASK_STRUCT_ALLOCATOR.
IA-64 was removed with commit cf8e865 ("arch: Remove Itanium (IA-64)
architecture"). Therefore remove support for ARCH_THREAD_STACK_ALLOCATOR
as well.

Link: https://lkml.kernel.org/r/20231116133638.1636277-3-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/Kconfig

@@ -305,13 +305,8 @@ config ARCH_HAS_CPU_FINALIZE_INIT
 config ARCH_TASK_STRUCT_ON_STACK
 	bool
 
-# Select if arch has its private alloc_task_struct() function
-config ARCH_TASK_STRUCT_ALLOCATOR
-	bool
-
 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	bool
-	depends on !ARCH_TASK_STRUCT_ALLOCATOR
 	help
 	  An architecture should select this to provide hardened usercopy
 	  knowledge about what region of the thread_struct should be

kernel/fork.c

@@ -165,7 +165,6 @@ void __weak arch_release_task_struct(struct task_struct *tsk)
 {
 }
 
-#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 static struct kmem_cache *task_struct_cachep;
 
 static inline struct task_struct *alloc_task_struct_node(int node)
@@ -177,7 +176,6 @@ static inline void free_task_struct(struct task_struct *tsk)
 {
 	kmem_cache_free(task_struct_cachep, tsk);
 }
-#endif
 
 /*
  * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
@@ -1001,7 +999,6 @@ static void set_max_threads(unsigned int max_threads_suggested)
 int arch_task_struct_size __read_mostly;
 #endif
 
-#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 static void task_struct_whitelist(unsigned long *offset, unsigned long *size)
 {
 	/* Fetch thread_struct whitelist for the architecture. */
@@ -1016,12 +1013,10 @@ static void task_struct_whitelist(unsigned long *offset, unsigned long *size)
 	else
 		*offset += offsetof(struct task_struct, thread);
 }
-#endif /* CONFIG_ARCH_TASK_STRUCT_ALLOCATOR */
 
 void __init fork_init(void)
 {
 	int i;
-#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 #ifndef ARCH_MIN_TASKALIGN
 #define ARCH_MIN_TASKALIGN	0
 #endif
@@ -1034,7 +1029,6 @@ void __init fork_init(void)
 			arch_task_struct_size, align,
 			SLAB_PANIC|SLAB_ACCOUNT,
 			useroffset, usersize, NULL);
-#endif
 
 	/* do the arch specific task caches init */
 	arch_task_cache_init();