Re: [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threadstrainwreck
From: Paul E. McKenney
Date: Wed Jul 20 2011 - 16:33:23 EST
On Wed, Jul 20, 2011 at 09:57:42PM +0200, Ingo Molnar wrote:
> * 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).
RCU_BOOST is currently default=n. Is that sufficient? If not, one
low-risk approach would be for me to just remove RCU_BOOST from init/Kconfig
in 3.0 and add it back in for 3.1. Please let me know what works best.
> 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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