linux-kernel - Re: RCU used on incoming CPU before rcu_cpu

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Date:   Thu, 9 Mar 2017 14:08:23 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, fweisbec@...il.com
Subject: Re: RCU used on incoming CPU before rcu_cpu_starting() called

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