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Date: Tue, 11 Nov 2008 11:00:50 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: adobriyan@...il.com, kenchen@...gle.com,
linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
Arjan van de Ven <arjan@...radead.org>
Subject: Re: [patch] add /proc/pid/stack to dump task's stack trace
* Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Fri, 7 Nov 2008 10:29:02 +0100
> Ingo Molnar <mingo@...e.hu> wrote:
>
> > > I guess the 0400 mode on that file will suffice...
> >
> > correct, 0400 is used already in the present patch:
> >
> > phoenix:~> cat /proc/1/stack
> > cat: /proc/1/stack: Permission denied
> >
> > but that is _not_ enough, it should be narrowed even more, to the
> > boundaries that i pointed out in my first review feedback mail, and
> > which is not implemented yet:
> >
> > 1) only root should be allowed to do this - i.e. file needs to be
> > root-owned.
> >
> > 2) there also needs to be a .config entry for folks to be able to
> > turn it off altogether - just like folks can turn off sysrq-t
> > dumping via the .config.
>
> Doing the above is desirable for another reason: given our rather
> erratic history with the stack backtracer, this /proc file is
> possibly a convenient way of oopsing the kernel, sending of off into
> la-la-land, etc.
the stack tracer is rock-solid on x86 since Arjan started cleaning up
the backtracing mess which we indeed had in x86 for years:
- adding frame-pointer support to 64-bit to improve the
quality of stack-traces
- eliminating the broken and fragile dwarf2-unwinder
- expanding the use of the generic stacktrace infrastructure to
lockdep, ftrace and other areas of code
if you know about any remaining fragility please holler, we havent had
a backtracer induced oops for a long time :-)
Ingo
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