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

Thomas Gleixner
2017-03-09T13:08:35Z

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.

Peter????

Thanks,

tglx