lkml.org 
[lkml]   [2008]   [Aug]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)
* Steven Rostedt (rostedt@goodmis.org) wrote:
>
> On Mon, 18 Aug 2008, Mathieu Desnoyers wrote:
>
> > * Steven Rostedt (rostedt@goodmis.org) wrote:
> > >
> > > On Tue, 19 Aug 2008, Benjamin Herrenschmidt wrote:
> > >
> > > >
> > > > > Hmm, this was originally copied from x86, where we did a cmpxchg, but that
> > > > > is probably not needed since all of this is done in kstop_machine. Also,
> > > > > only the "get" is needed. If we don't fault there, we wont fault on the
> > > > > put (unless we have permissions wrong, and that would be a bug).
> > > >
> > > > Would it ? How do we make sure the kernel text is mapped writeable ?
> > >
> > > We map it writeable if FTRACE is enabled.
> > >
> >
> > Argh. See text_poke(). It's there exactly for this purpose on x86.
>
> Ouch, I just did. text_poke is quite heavy. It would be interesting to see
> that performed on 20,000 locations at one time. I could play with it, but
> I'm a bit nervous.
>

It's alread used to modify the LOCK prefixes in alternative.c and did
not seem to be too slow for that.. it should therefore be ok.

Mathieu

> -- Steve

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


\
 
 \ /
  Last update: 2008-08-19 05:43    [W:0.367 / U:0.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site