linux-kernel - Re: [PATCH 2/8] kernel/fork: Duplicate task

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Message-ID: <8340d413-4951-5e62-ef5f-f396523edac7@kernel.org>
Date:   Fri, 11 Feb 2022 15:42:38 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org
Cc:     Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH 2/8] kernel/fork: Duplicate task_struct before stack
 allocation.

On 1/25/22 07:26, Sebastian Andrzej Siewior wrote:
> 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.

I understand the problem, I think.

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

But I don't understand this.  How does this patch relate to the problem?

Also, you appear to be missing a change to the free_stack and free_tsk 
code at the end of dup_task_struct().