| Message ID | 20110819163547.GA5182@linux.vnet.ibm.com |
|---|---|
| State | New |
| Headers | show |
On Fri, Aug 19, 2011 at 09:35:47AM -0700, Paul E. McKenney wrote: > CPUs set rdp->qs_pending when coming online to resolve races with > grace-period start. However, this means that if RCU is idle, the > just-onlined CPU might needlessly send itself resched IPIs. Adjust the > online-CPU initialization to avoid this, and also to correctly cause > the CPU to respond to the current grace period if needed. > > This patch is believed to fix or otherwise suppress problems in > https://bugzilla.redhat.com/show_bug.cgi?id=726877, however, the > relationship is not apparent to this patch's author. That said, it is > hard to argue with test results. > > This will be available from -rcu as soon as kernel.org's mirrors update: > > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git rcu/urgent > > Reported-by: Nicolas Mailhot <nicolas.mailhot@laposte.net> > Reported-by: Michal Jaegermann <michal@harddata.com> > Reported-by: Josh Boyer <jwboyer@redhat.com> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Tested-by: Josh Boyer <jwboyer@redhat.com> > > rcutree.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > <formletter> This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read Documentation/stable_kernel_rules.txt for how to do this properly. </formletter>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index ba06207..39cc360 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1865,8 +1865,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) /* Set up local state, ensuring consistent view of global state. */ raw_spin_lock_irqsave(&rnp->lock, flags); - rdp->passed_quiesc = 0; /* We could be racing with new GP, */ - rdp->qs_pending = 1; /* so set up to respond to current GP. */ rdp->beenonline = 1; /* We have now been online. */ rdp->preemptible = preemptible; rdp->qlen_last_fqs_check = 0; @@ -1891,8 +1889,15 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) rnp->qsmaskinit |= mask; mask = rnp->grpmask; if (rnp == rdp->mynode) { - rdp->gpnum = rnp->completed; /* if GP in progress... */ + /* + * If there is a grace period in progress, we will + * set up to wait for it next time we run the + * RCU core code. + */ + rdp->gpnum = rnp->completed; rdp->completed = rnp->completed; + rdp->passed_quiesc = 0; + rdp->qs_pending = 0; rdp->passed_quiesc_completed = rnp->completed - 1; } raw_spin_unlock(&rnp->lock); /* irqs already disabled. */