It turns out that it is queue_delayed_work_on() rather than queue_work_on() that has difficulties when used concurrently with CPU-hotplug removal operations. It is therefore unnecessary to protect CPU identification and queue_work_on() with preempt_disable().
This commit therefore removes the preempt_disable() and preempt_enable() from sync_rcu_exp_select_cpus(), which has the further benefit of reducing the number of changes that must be maintained in the -rt patchset. Reported-by: Thomas Gleixner <[email protected]> Reported-by: Sebastian Siewior <[email protected]> Suggested-by: Boqun Feng <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/rcu/tree_exp.h | 2 -- 1 file changed, 2 deletions(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 928fe5893a57..f42c999f4d2d 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -449,7 +449,6 @@ static void sync_rcu_exp_select_cpus(smp_call_func_t func) continue; } INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus); - preempt_disable(); cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1); /* If all offline, queue the work on an unbound CPU. */ if (unlikely(cpu > rnp->grphi - rnp->grplo)) @@ -457,7 +456,6 @@ static void sync_rcu_exp_select_cpus(smp_call_func_t func) else cpu += rnp->grplo; queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work); - preempt_enable(); rnp->exp_need_flush = true; } -- 2.17.1
