[PATCH] Documentation: x86: update the thread_info's position

[PATCH] Documentation: x86: update the thread_info's position

[Mingzhe Yang]

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@gmail.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).
 
 In addition to the per thread stacks, there are specialized stacks
 associated with each CPU.  These stacks are only used while the kernel
-- 
1.8.3.1

Re: [PATCH] Documentation: x86: update the thread_info's position

[Jonathan Corbet]

On Sat,  5 Dec 2020 13:01:36 +0800
Mingzhe Yang <cainiao666999@gmail.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@gmail.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

Re: [PATCH] Documentation: x86: update the thread_info's position

[Mingzhe Yang]

Thanks a million!
I truly appreciate your review!

On Tue, Dec 22, 2020 at 12:57 AM Jonathan Corbet <corbet@lwn.net> wrote:
>
> On Sat,  5 Dec 2020 13:01:36 +0800
> Mingzhe Yang <cainiao666999@gmail.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@gmail.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