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SubjectRe: cpu stopper threads and load balancing leads to deadlock
On Thu, May 17, 2018 at 04:23:22PM +0200, Peter Zijlstra wrote:
> On Thu, May 17, 2018 at 07:03:45AM -0700, Paul E. McKenney wrote:
> > On Tue, May 15, 2018 at 06:30:26AM +0200, Mike Galbraith wrote:
> > I have not queued it, but given Peter's Signed-off-by and your Tested-by
> > I would be happy to do so.
>
> And a Changelog of course :-)

Thank you both!

Is this OK for 4.19, or do we need it for 4.18? I am guessing 4.18,
but figured I should ask before wildly rebasing the 82 commits destined
for 4.19. ;-)

Thanx, Paul

> ---
> From: Peter Zijlstra <peterz@infradead.org>
> Subject: rcu/x86: Provide early rcu_cpu_starting() callback
>
> The x86/mtrr code does horrific things because hardware. It uses
> stop_machine_from_inactive_cpu(), which does a wakeup (of the stopper
> thread on another CPU), which uses RCU, all before the CPU is onlined.
>
> RCU complains about this, because wakeups use RCU and RCU does
> (rightfully) not consider offline CPUs for grace-periods.
>
> Fix this by initializing RCU way early in the MTRR case.
>
> Tested-by: Mike Galbraith <efault@gmx.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>
> > > > diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
> > > > index 7468de429087..07360523c3ce 100644
> > > > --- a/arch/x86/kernel/cpu/mtrr/main.c
> > > > +++ b/arch/x86/kernel/cpu/mtrr/main.c
> > > > @@ -793,6 +793,9 @@ void mtrr_ap_init(void)
> > > >
> > > > if (!use_intel() || mtrr_aps_delayed_init)
> > > > return;
> > > > +
> > > > + rcu_cpu_starting(smp_processor_id());
> > > > +
> > > > /*
> > > > * Ideally we should hold mtrr_mutex here to avoid mtrr entries
> > > > * changed, but this routine will be called in cpu boot time,
> > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > > index 2a734692a581..4dab46950fdb 100644
> > > > --- a/kernel/rcu/tree.c
> > > > +++ b/kernel/rcu/tree.c
> > > > @@ -3775,6 +3775,8 @@ int rcutree_dead_cpu(unsigned int cpu)
> > > > return 0;
> > > > }
> > > >
> > > > +static DEFINE_PER_CPU(int, rcu_cpu_started);
> > > > +
> > > > /*
> > > > * Mark the specified CPU as being online so that subsequent grace periods
> > > > * (both expedited and normal) will wait on it. Note that this means that
> > > > @@ -3796,6 +3798,11 @@ void rcu_cpu_starting(unsigned int cpu)
> > > > struct rcu_node *rnp;
> > > > struct rcu_state *rsp;
> > > >
> > > > + if (per_cpu(rcu_cpu_started, cpu))
> > > > + return;
> > > > +
> > > > + per_cpu(rcu_cpu_started, cpu) = 1;
> > > > +
> > > > for_each_rcu_flavor(rsp) {
> > > > rdp = per_cpu_ptr(rsp->rda, cpu);
> > > > rnp = rdp->mynode;
> > > > @@ -3852,6 +3859,8 @@ void rcu_report_dead(unsigned int cpu)
> > > > preempt_enable();
> > > > for_each_rcu_flavor(rsp)
> > > > rcu_cleanup_dying_idle_cpu(cpu, rsp);
> > > > +
> > > > + per_cpu(rcu_cpu_started, cpu) = 0;
> > > > }
> > > >
> > > > /* Migrate the dead CPU's callbacks to the current CPU. */
> > >
> >
>

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