linux-kernel - Re: [PATCH] Documentation: x86: update the thread

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Message-ID: <20201221095721.6bebfb28@lwn.net>
Date:   Mon, 21 Dec 2020 09:57:21 -0700
From:   Jonathan Corbet <corbet@....net>
To:     Mingzhe Yang <cainiao666999@...il.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, David.Laight@...lab.com
Subject: Re: [PATCH] Documentation: x86: update the thread_info's position

On Sat,  5 Dec 2020 13:01:36 +0800
Mingzhe Yang <cainiao666999@...il.com> wrote:

> Prior to kernel 4.9 the thread_info structure was at the bottom of
> the kernel stack. kernel 4.9 moved it into the task_struct.
> 
> See commits c65eacb ("sched/core: Allow putting thread_info into
> task_struct"), 15f4eae ("x86: Move thread_info into task_struct")
> and 883d50f ("scripts/gdb: fix get_thread_info").
> 
> Signed-off-by: Mingzhe Yang <cainiao666999@...il.com>
> ---
>  Documentation/x86/kernel-stacks.rst | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/x86/kernel-stacks.rst b/Documentation/x86/kernel-stacks.rst
> index 6b0bcf0..e9097f3 100644
> --- a/Documentation/x86/kernel-stacks.rst
> +++ b/Documentation/x86/kernel-stacks.rst
> @@ -15,7 +15,8 @@ Like all other architectures, x86_64 has a kernel stack for every
>  active thread.  These thread stacks are THREAD_SIZE (2*PAGE_SIZE) big.
>  These stacks contain useful data as long as a thread is alive or a
>  zombie. While the thread is in user space the kernel stack is empty
> -except for the thread_info structure at the bottom.
> +except for the thread_info structure at the bottom (since kernel 4.9,
> +the thread_info structure has been moved into task_struct).

So this has been sitting in my inbox for a bit, sorry.  This seems worth
fixing, but is this the correct fix?  The documentation should reflect the
current kernel, rather than what once was with a "(it's not actually that
way anymore)" note.  Is the kernel stack truly empty now?  If so we should
just say that; otherwise say what's lurking there in current kernels.

Thanks,

jon