From 2af196c228bce68f190b03cf2613f14635efaabe Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 17 Feb 2022 11:24:00 +0100
Subject: [PATCH] kernel/fork: Duplicate task_struct before stack allocation.

References: SLE Realtime Extension
Patch-mainline: v5.18-rc1
Git-commit: 546c42b2c5c161619736dd730d3df709181999d0

alloc_thread_stack_node() already populates the task_struct::stack
member except on IA64. The stack pointer is saved and populated again
because IA64 needs it and arch_dup_task_struct() overwrites it.

Allocate thread's stack after task_struct has been duplicated as a
preparation.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20220217102406.3697941-3-bigeasy@linutronix.de
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 kernel/fork.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index c56b92cab976..a60d7d928e86 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -876,6 +876,10 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 	if (!tsk)
 		return NULL;
 
+	err = arch_dup_task_struct(tsk, orig);
+	if (err)
+		goto free_tsk;
+
 	stack = alloc_thread_stack_node(tsk, node);
 	if (!stack)
 		goto free_tsk;
@@ -885,8 +889,6 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 
 	stack_vm_area = task_stack_vm_area(tsk);
 
-	err = arch_dup_task_struct(tsk, orig);
-
 	/*
 	 * arch_dup_task_struct() clobbers the stack-related fields.  Make
 	 * sure they're properly initialized before using any stack-related
@@ -900,9 +902,6 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 	refcount_set(&tsk->stack_refcount, 1);
 #endif
 
-	if (err)
-		goto free_stack;
-
 	err = scs_prepare(tsk, node);
 	if (err)
 		goto free_stack;