From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Ben Greear <greearb@candelatech.com>
Cc: Ingo Molnar <mingo@elte.hu>,
Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>, Ed Tomlinson <edt@aei.ca>,
linux-kernel@vger.kernel.org, laijs@cn.fujitsu.com,
dipankar@in.ibm.com, akpm@linux-foundation.org,
mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org,
niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org,
Valdis.Kletnieks@vt.edu, dhowells@redhat.com,
eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org,
edward.tomlinson@aero.bombardier.com
Subject: Re: [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck
Date: Wed, 20 Jul 2011 14:12:17 -0700 [thread overview]
Message-ID: <20110720211217.GS2313@linux.vnet.ibm.com> (raw)
In-Reply-To: <4E274099.20704@candelatech.com>
On Wed, Jul 20, 2011 at 01:54:49PM -0700, Ben Greear wrote:
> On 07/20/2011 01:33 PM, Paul E. McKenney wrote:
> >On Wed, Jul 20, 2011 at 09:57:42PM +0200, Ingo Molnar wrote:
> >>
> >>* Ingo Molnar<mingo@elte.hu> wrote:
> >>
> >>>
> >>>* Paul E. McKenney<paulmck@linux.vnet.ibm.com> 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
>
> Not if it remains broken I think..unless you put it under CONFIG_BROKEN
> or something. Otherwise, folks are liable to turn it on and not realize
> it's the cause of subtle bugs.
Good point, I could easily add "depends on BROKEN".
> For what it's worth, my tests have been running clean for around 2 hours, so the full set of
> fixes with RCU_BOOST appears good, so far. I'll let it continue to run
> at least overnight to make sure I'm not just getting lucky...
Continuing to think good thoughts... ;-)
Thanx, Paul
next prev parent reply other threads:[~2011-07-20 21:25 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-20 0:17 [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 1/7] rcu: decrease rcu_report_exp_rnp coupling with scheduler Paul E. McKenney
2011-07-20 2:40 ` Peter Zijlstra
2011-07-20 4:54 ` Paul E. McKenney
2011-07-20 11:23 ` Ed Tomlinson
2011-07-20 11:31 ` Ed Tomlinson
2011-07-20 12:35 ` Peter Zijlstra
2011-07-20 13:23 ` Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 2/7] rcu: Fix RCU_BOOST race handling current->rcu_read_unlock_special Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 3/7] rcu: Streamline code produced by __rcu_read_unlock() Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 4/7] rcu: protect __rcu_read_unlock() against scheduler-using irq handlers Paul E. McKenney
2011-07-20 12:54 ` Peter Zijlstra
2011-07-20 13:25 ` Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 5/7] sched: Add irq_{enter,exit}() to scheduler_ipi() Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 6/7] softirq,rcu: Inform RCU of irq_exit() activity Paul E. McKenney
2011-07-20 0:18 ` [PATCH tip/core/urgent 7/7] signal: align __lock_task_sighand() irq disabling and RCU Paul E. McKenney
2011-07-20 1:10 ` [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck Ben Greear
2011-07-20 1:30 ` Ed Tomlinson
2011-07-20 2:07 ` Ed Tomlinson
2011-07-20 4:44 ` Paul E. McKenney
2011-07-20 5:03 ` Linus Torvalds
2011-07-20 13:34 ` Paul E. McKenney
2011-07-20 17:02 ` Ben Greear
2011-07-20 17:15 ` Paul E. McKenney
2011-07-20 18:44 ` Ingo Molnar
2011-07-20 18:52 ` Peter Zijlstra
2011-07-20 19:01 ` Paul E. McKenney
2011-07-20 19:25 ` Peter Zijlstra
2011-07-20 20:06 ` Paul E. McKenney
2011-07-20 19:02 ` Linus Torvalds
2011-07-20 19:29 ` Paul E. McKenney
2011-07-20 19:39 ` Ingo Molnar
2011-07-20 19:57 ` Ingo Molnar
2011-07-20 20:33 ` Paul E. McKenney
2011-07-20 20:54 ` Ben Greear
2011-07-20 21:12 ` Paul E. McKenney [this message]
2011-07-21 3:25 ` Ben Greear
2011-07-21 16:04 ` Paul E. McKenney
2011-07-20 21:04 ` [GIT PULL] RCU fixes for v3.0 Ingo Molnar
2011-07-20 21:55 ` Ed Tomlinson
2011-07-20 22:06 ` Paul E. McKenney
2011-07-20 20:08 ` [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck Paul E. McKenney
2011-07-20 21:05 ` Peter Zijlstra
2011-07-20 21:39 ` Paul E. McKenney
2011-07-20 10:49 ` Ed Tomlinson
2011-07-20 18:25 ` [PATCH rcu/urgent 0/7 v2] " Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 1/7] rcu: decrease rcu_report_exp_rnp coupling with scheduler Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 2/7] rcu: Fix RCU_BOOST race handling current->rcu_read_unlock_special Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 3/7] rcu: Streamline code produced by __rcu_read_unlock() Paul E. McKenney
2011-07-20 22:44 ` Linus Torvalds
2011-07-21 5:09 ` Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 4/7] rcu: protect __rcu_read_unlock() against scheduler-using irq handlers Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 5/7] sched: Add irq_{enter,exit}() to scheduler_ipi() Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 6/7] softirq,rcu: Inform RCU of irq_exit() activity Paul E. McKenney
2011-07-20 18:26 ` [PATCH tip/core/urgent 7/7] signal: align __lock_task_sighand() irq disabling and RCU Paul E. McKenney
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