Re: [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threadstrainwreck

From: Ingo Molnar
Date: Wed Jul 20 2011 - 15:59:20 EST

* Ingo Molnar <mingo@xxxxxxx> wrote:

> * Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> > If my guess is correct, then the minimal non-RCU_BOOST fix is #4
> > (which drags along #3) and #6. Which are not one-liners, but
> > somewhat smaller:
> >
> > b/kernel/rcutree_plugin.h | 12 ++++++------
> > b/kernel/softirq.c | 12 ++++++++++--
> > kernel/rcutree_plugin.h | 31 +++++++++++++++++++++++++------
> > 3 files changed, 41 insertions(+), 14 deletions(-)
> That's half the patch size and half the patch count.
> PeterZ's question is relevant: since we apparently had similar bugs
> in v2.6.39 as well, what changed in v3.0 that makes them so urgent
> to fix?
> If it's just better instrumentation that proves them better then
> i'd suggest fixing this in v3.1 and not risking v3.0 with an
> unintended side effect.

Ok, i looked some more at the background and the symptoms that people
are seeing: kernel crashes and lockups. I think we want these
problems fixed in v3.0, even if it was the recent introduction of
RCU_BOOST that made it really prominent.

Having put some testing into your rcu/urgent branch today i'd feel
more comfortable with taking this plus perhaps an RCU_BOOST disabling
patch. That makes it all fundamentally tested by a number of people
(including those who reported/reproduced the problems).

Linus, would that approach be fine with you? I'll send an RFC pull
request for the 6 patches as a reply to this mail, in a couple of


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