On Mon, Aug 26, 2013 at 01:30:41PM -0400, Steven Rostedt wrote:
> > On Mon, Aug 26, 2013 at 10:58:38AM -0400, Dave Jones wrote:
> > > Another day, another rcu backtrace..
> > > This says rc6, but it's pretty darn close to rc7, I think it was running
> > > a build from Friday.
> >
> > Could you please send your .config? Also, were you running ftrace,
> > perf, RCU event tracing, or what?
> >
> > Looks like you are running ftrace, but I though Steven had set that
> > up so that it could be called from an extended quiescent state.
> >
>
> I know exactly what the issue is. Yes ftrace is safe to call even from
> these extended quiescent states, the problem is that ftrace is also the
> infrastructure of other users, where some of those users are not safe.
> Namely, perf.
>
> Right now perf is not safe to trace all functions, as some of those
> functions have this issue. I was going to add something like:
>
> FTRACE_NON_SAFE(rcu_eqs_enter);
>
> where it will record locations that are not safe for all users, such
> that unless a function registers to ftrace with a flag of
> "FTRACE_FL_NON_SAFE_OK", anything that is on the non safe list (from
> the macro) will not be traced.
>
> Now, how urgent is this fix? perf can only trace functions as root, and
> there's no reason for perf to be tracing all functions at the moment.
> But yes, a root user could run that and get this warning. Because I was
> going to implement this for 3.12 and not for this release.
This was triggered as a regular user fwiw.
I had not been running perf, or any other tracing. It was just left
fuzzing over the weekend with no interaction at all.
Dave
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
