Re: RCU used on incoming CPU before rcu_cpu_starting() called

Paul E. McKenney
2017-03-09T15:25:20Z

On Thu, Mar 09, 2017 at 02:08:23PM +0100, Thomas Gleixner wrote:
> On Wed, 8 Mar 2017, Paul E. McKenney wrote:
> > [ 30.694013] lockdep_rcu_suspicious+0xe7/0x120
> > [ 30.694013] get_work_pool+0x82/0x90
> > [ 30.694013] __queue_work+0x70/0x5f0
> > [ 30.694013] queue_work_on+0x33/0x70
> > [ 30.694013] clear_sched_clock_stable+0x33/0x40
> > [ 30.694013] early_init_intel+0xe7/0x2f0
> > [ 30.694013] init_intel+0x11/0x350
> > [ 30.694013] identify_cpu+0x344/0x5a0
> > [ 30.694013] identify_secondary_cpu+0x18/0x80
> > [ 30.694013] smp_store_cpu_info+0x39/0x40
> > [ 30.694013] start_secondary+0x4e/0x100
> > [ 30.694013] start_cpu+0x14/0x14
> >
> > Here is the relevant code from x86's smp_callin():
> >
> > /*
> > * Save our processor parameters. Note: this information
> > * is needed for clock calibration.
> > */
> > smp_store_cpu_info(cpuid);
> >
> > The problem is that smp_store_cpu_info() indirectly invokes
> > schedule_work(), which wants to use RCU. But RCU isn't informed
> > of the incoming CPU until the call to notify_cpu_starting(), which
> > causes lockdep to complain bitterly about the use of RCU by the
> > premature call to schedule_work().
>
> Right. And that want's to be fixed, not hacked around by silencing RCU.

Fair enough!

I have updated my commit to indicate yours and Frederic's discomfort with
it and marked it as not intended for upstream. If we get an alternative
fix shortly, I will drop my commit -- but failing that at some point I
will of course start pushing this patch again.

Thanx, Paul

> Peter????
>
> Thanks,
>
> tglx
>