linux-kernel - Re: [PATCH] proc: remove /proc/*/status "Stack usage:"

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Date:	Mon, 02 Nov 2009 11:13:10 +0100
From:	Stefani Seibold <stefani@...bold.net>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] proc: remove /proc/*/status "Stack usage:"


> Poor embedded people!
> 

That's why embedded peoble don't like to contribute their work.

> There is even Documentation/vm/page-types.c which is trivially adapted
> to show stack pages state.
> 
> > Like Dr Frank. N. Furter in the "Rocky Horror Picture Show" says: remove
> > the cause but NOT the symptoms!
> 
> The root of the problem is that you're measuring badly defined value.
> 
> Kernel doesn't know SP register of a running task until it stops it.
> Even if task is stopped or inside kernel, kernel doesn't know where
> userpace stack starts, because, in theory, application can move it's
> stack to anywhere.
> 

It works fine for 99% percent of the use cases. Nothing is perfect,
especially in theory.

> > And the cause is the miss implemented KSTK_ESP in a x86_64. I also
> > checked all other architekture depended KSTK_ESP definitions and this
> > definitions looks okay for me. 

BTW: I had fixed the x86_65 KSTP_ESP implementation. I tested it with 32
bit and 64 bit user space application. I will send soon a patch. Thanks
for figure out the problem.

Stefani


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