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From:   Heiko Carstens <hca@linux.ibm.com>
To:     Ard Biesheuvel <ardb@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH 3/3] arch: remove ARCH_TASK_STRUCT_ON_STACK
Date:   Thu, 16 Nov 2023 14:36:38 +0100
Message-Id: <20231116133638.1636277-4-hca@linux.ibm.com>
In-Reply-To: <20231116133638.1636277-1-hca@linux.ibm.com>
References: <20231116133638.1636277-1-hca@linux.ibm.com>
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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.

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
 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(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index c2f87ef9f0ae..bfcc7c2dc039 100644
--- a/arch/Kconfig
+++ b/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
diff --git a/arch/powerpc/kexec/core_64.c b/arch/powerpc/kexec/core_64.c
index 0bee7ca9a77c..762e4d09aacf 100644
--- a/arch/powerpc/kexec/core_64.c
+++ b/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
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 40fc5813cf93..bccb3f1f6262 100644
--- a/include/linux/init_task.h
+++ b/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")
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 292c31697248..c2ecb2e06046 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1955,9 +1955,7 @@ extern void ia64_set_curr_task(int cpu, struct task_struct *p);
 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
diff --git a/init/init_task.c b/init/init_task.c
index 5727d42149c3..6f6485d554df 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -51,8 +51,7 @@ static struct sighand_struct init_sighand = {
 };
 
 #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_SIZE / sizeof(long)]
  * 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),
-- 
2.39.2