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Date: Tue, 12 Jul 2011 14:29:20 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Julie Sullivan <kernelmail.jms@...il.com> Cc: linux-kernel-mail <linux-kernel@...r.kernel.org> Subject: Re: PROBLEM: 3.0-rc kernels unbootable since -rc3 On Tue, Jul 12, 2011 at 10:15:40PM +0100, Julie Sullivan wrote: > On Mon, Jul 11, 2011 at 10:43 PM, Paul E. McKenney > <paulmck@...ux.vnet.ibm.com> wrote: > > On Mon, Jul 11, 2011 at 09:37:53PM +0100, julie Sullivan wrote: > >> > And here is what I am proposing sending upstream. I have your Tested-by, > >> > but had to make a small but very real change in order to make it work > >> > under all configurations that I test under. So could you please try > >> > the attached patch out? I am particularly interested in how it works > >> > out when CONFIG_RCU_BOOST=n. > >> > > >> > Thanx, Paul > >> > > >> > ------------------------------------------------------------------------ > >> > > >> > rcu: Prevent RCU callbacks from executing during early boot > >> > > >> > Under some rare but real combinations of configuration parameters, RCU > >> > callbacks are posted during early boot that use kernel facilities that > >> > are not yet initialized. Therefore, when these callbacks are invoked, > >> > hard hangs and crashes ensue. This commit therefore prevents RCU > >> > callbacks from being invoked until after the scheduler is up and running. > >> > > >> > It might well turn out that a better approach is to identify the specific > >> > RCU callbacks that are causing this problem, but that discussion will > >> > wait until such time as someone really needs an RCU callback to be > >> > invoked during early boot. > >> > > >> > Reported-by: julie Sullivan <kernelmail.jms@...il.com> > >> > Tested-by: julie Sullivan <kernelmail.jms@...il.com> > >> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > >> > > >> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > >> > index 7e59ffb..4c0210f 100644 > >> > --- a/kernel/rcutree.c > >> > +++ b/kernel/rcutree.c > >> > @@ -1467,7 +1467,7 @@ static void rcu_process_callbacks(struct softirq_action *unused) > >> > */ > >> > static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) > >> > { > >> > - if (likely(!rsp->boost)) { > >> > + if (likely(rcu_scheduler_active && !rsp->boost)) { > >> > rcu_do_batch(rsp, rdp); > >> > return; > >> > } > >> > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > >> > index 14dc7dd..ca3c6dc 100644 > >> > --- a/kernel/rcutree_plugin.h > >> > +++ b/kernel/rcutree_plugin.h > >> > @@ -1703,7 +1703,7 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) > >> > > >> > static void invoke_rcu_callbacks_kthread(void) > >> > { > >> > - WARN_ON_ONCE(1); > >> > + WARN_ON_ONCE(rcu_scheduler_active); > >> > } > >> > > >> > static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) > >> > > >> > >> Hi Paul, > >> Is this to be applied on a clean v3.0-rc4? I tried this but I'm afraid > >> the boot crash is back again (on -rc5 and -rc6 too). > > > > I must confess that it did seem to be giving up a bit too easily. :-( > > > > So, I have created a new branch jms.2011.07.11a on the -rcu git tree at: > > > > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git > > > > If the new branch jms.2011.07.11a fails and the old branch jms.2011.07.07a > > succeeds (both with CONFIG_RCU_BOOST=n), then that indicates that my > > mainlinable patch didn't delay the callbacks quite far enough. On the > > other hand, if both succeed, then that means that there is another bug > > lurking later on in the sequence of commits. > > > > Could you please test these out? > > > > Thanx, Paul > > > > OK tested- jms.2011.07.11a fails. The other one's fine (I'm actually > running an -rc6 with its patches right now :-) Just to make sure I understand what patch you are using... Is it the one that I have listed below? It would be bad form for me to send the wrong patch upstream. ;-) If this is the correct one, then the upstreamable patch I sent recently (https://lkml.org/lkml/2011/7/12/313) should also work. Famous last words... Thanx, Paul ------------------------------------------------------------------------ rcu: prevent RCU callbacks from being invoked during early boot. Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> diff --git a/kernel/rcutree.c b/kernel/rcutree.c index dbe4120..4456395 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1476,7 +1476,7 @@ static void rcu_process_callbacks(struct softirq_action *unused) */ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) { - if (likely(!rsp->boost)) { + if (likely(rcu_kthreads_spawnable && !rsp->boost)) { rcu_do_batch(rsp, rdp); return; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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