+ arch-remove-arch_task_struct_on_stack.patch added to mm-nonmm-unstable branch

+ arch-remove-arch_task_struct_on_stack.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: arch: remove ARCH_TASK_STRUCT_ON_STACK
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     arch-remove-arch_task_struct_on_stack.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/arch-remove-arch_task_struct_on_stack.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Heiko Carstens <hca@linux.ibm.com>
Subject: arch: remove ARCH_TASK_STRUCT_ON_STACK
Date: Thu, 16 Nov 2023 14:36:38 +0100

IA-64 was the only architecture which selected ARCH_TASK_STRUCT_ON_STACK.
IA-64 was removed with commit cf8e8658100d ("arch: Remove Itanium (IA-64)
architecture"). Therefore remove support for ARCH_TASK_STRUCT_ON_STACK
as well.

Note: this also reveals a potential bug in powerpc code, which makes use of
__init_task_data without selecting ARCH_TASK_STRUCT_ON_STACK which makes
__init_task_data a no-op. This is broken since commit d11ed3ab3166 ("Expand
INIT_TASK() in init/init_task.c and remove") from 2018 and needs to be
addressed separately.

Link: https://lkml.kernel.org/r/20231116133638.1636277-4-hca@linux.ibm.com
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/Kconfig                 |    4 ----
 arch/powerpc/kexec/core_64.c |    3 +--
 include/linux/init_task.h    |    7 -------
 include/linux/sched.h        |    2 --
 init/init_task.c             |   10 ++--------
 5 files changed, 3 insertions(+), 23 deletions(-)

--- a/arch/Kconfig~arch-remove-arch_task_struct_on_stack
+++ a/arch/Kconfig
@@ -301,10 +301,6 @@ config ARCH_HAS_DMA_CLEAR_UNCACHED
 config ARCH_HAS_CPU_FINALIZE_INIT
 	bool
 
-# Select if arch init_task must go in the __init_task_data section
-config ARCH_TASK_STRUCT_ON_STACK
-	bool
-
 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	bool
 	help
--- a/arch/powerpc/kexec/core_64.c~arch-remove-arch_task_struct_on_stack
+++ a/arch/powerpc/kexec/core_64.c
@@ -283,8 +283,7 @@ static void kexec_prepare_cpus(void)
  * We could use a smaller stack if we don't care about anything using
  * current, but that audit has not been performed.
  */
-static union thread_union kexec_stack __init_task_data =
-	{ };
+static union thread_union kexec_stack = { };
 
 /*
  * For similar reasons to the stack above, the kexecing CPU needs to be on a
--- a/include/linux/init_task.h~arch-remove-arch_task_struct_on_stack
+++ a/include/linux/init_task.h
@@ -37,13 +37,6 @@ extern struct cred init_cred;
 
 #define INIT_TASK_COMM "swapper"
 
-/* Attach to the init_task data structure for proper alignment */
-#ifdef CONFIG_ARCH_TASK_STRUCT_ON_STACK
-#define __init_task_data __section(".data..init_task")
-#else
-#define __init_task_data /**/
-#endif
-
 /* Attach to the thread_info data structure for proper alignment */
 #define __init_thread_info __section(".data..init_thread_info")
 
--- a/include/linux/sched.h~arch-remove-arch_task_struct_on_stack
+++ a/include/linux/sched.h
@@ -1955,9 +1955,7 @@ extern void ia64_set_curr_task(int cpu,
 void yield(void);
 
 union thread_union {
-#ifndef CONFIG_ARCH_TASK_STRUCT_ON_STACK
 	struct task_struct task;
-#endif
 #ifndef CONFIG_THREAD_INFO_IN_TASK
 	struct thread_info thread_info;
 #endif
--- a/init/init_task.c~arch-remove-arch_task_struct_on_stack
+++ a/init/init_task.c
@@ -51,8 +51,7 @@ static struct sighand_struct init_sighan
 };
 
 #ifdef CONFIG_SHADOW_CALL_STACK
-unsigned long init_shadow_call_stack[SCS_SIZE / sizeof(long)]
-		__init_task_data = {
+unsigned long init_shadow_call_stack[SCS_SIZE / sizeof(long)] = {
 	[(SCS_SIZE / sizeof(long)) - 1] = SCS_END_MAGIC
 };
 #endif
@@ -61,12 +60,7 @@ unsigned long init_shadow_call_stack[SCS
  * Set up the first task table, touch at your own risk!. Base=0,
  * limit=0x1fffff (=2MB)
  */
-struct task_struct init_task
-#ifdef CONFIG_ARCH_TASK_STRUCT_ON_STACK
-	__init_task_data
-#endif
-	__aligned(L1_CACHE_BYTES)
-= {
+struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 	.thread_info	= INIT_THREAD_INFO(init_task),
 	.stack_refcount	= REFCOUNT_INIT(1),
_

Patches currently in -mm which might be from hca@linux.ibm.com are

arch-remove-arch_thread_stack_allocator.patch
arch-remove-arch_task_struct_allocator.patch
arch-remove-arch_task_struct_on_stack.patch