Messages in this thread Patch in this message | | | Date | Thu, 3 May 2018 18:45:08 +0200 | From | Peter Zijlstra <> | Subject | Re: cpu stopper threads and load balancing leads to deadlock |
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On Thu, May 03, 2018 at 09:12:31AM -0700, Paul E. McKenney wrote: > On Thu, May 03, 2018 at 04:44:50PM +0200, Peter Zijlstra wrote: > > On Thu, May 03, 2018 at 04:16:55PM +0200, Mike Galbraith wrote: > > > On Thu, 2018-05-03 at 15:56 +0200, Peter Zijlstra wrote: > > > > On Thu, May 03, 2018 at 03:32:39PM +0200, Mike Galbraith wrote: > > > > > > > > > Dang. With $subject fix applied as well.. > > > > > > > > That's a NO then... :-( > > > > > > Could say who cares about oddball offline wakeup stat. <cringe> > > > > Yeah, nobody.. but I don't want to have to change the wakeup code to > > deal with this if at all possible. That'd just add conditions that are > > 'always' false, except in this exceedingly rare circumstance. > > > > So ideally we manage to tell RCU that it needs to pay attention while > > we're doing this here thing, which is what I thought RCU_NONIDLE() was > > about. > > One straightforward approach would be to provide a arch-specific > Kconfig option that tells notify_cpu_starting() not to bother invoking > rcu_cpu_starting(). Then x86 selects this Kconfig option and invokes > rcu_cpu_starting() itself early enough to avoid splats. > > See the (untested, probably does not even build) patch below. > > I have no idea where to insert either the "select" or the call to > rcu_cpu_starting(), so I left those out. I know that putting the > call too early will cause trouble, but I have no idea what constitutes > "too early". :-/
Something like so perhaps? Mike, can you play around with that? Could burn your granny and eat your cookies.
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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