From: Boqun Feng <[email protected]> Currently, the parallelized initialization of expedited grace periods uses the workqueue associated with each rcu_node structure's ->grplo field. This works fine unless that CPU is offline. This commit therefore uses the CPU corresponding to the lowest-numbered online CPU, or just reports the quiescent states if there are no online CPUs on this rcu_node structure.
Note that this patch uses cpu_is_offline() instead of the usual approach of checking bits in the rcu_node structure's ->qsmaskinitnext field. This is safe because preemption is disabled across both the cpu_is_offline() check and the call to queue_work_on(). Not-Yet-Signed-off-by: Boqun Feng <[email protected]> [ paulmck: Disable preemption to close offline race window. ] Not-Yet-Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/rcu/tree_exp.h | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index c6385ee1af65..6acac74092cb 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -472,6 +472,7 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, smp_call_func_t func) { + int cpu; struct rcu_node *rnp; trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("reset")); @@ -493,8 +494,19 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, continue; } INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus); - queue_work_on(rnp->grplo, rcu_par_gp_wq, &rnp->rew.rew_work); - rnp->exp_need_flush = true; + preempt_disable(); + for_each_leaf_node_possible_cpu(rnp, cpu) { + if (cpu_is_offline(cpu)) /* Preemption disabled. */ + continue; + queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work); + rnp->exp_need_flush = true; + break; + } + preempt_enable(); + if (!rnp->exp_need_flush) { /* All offline, report QSes. */ + queue_work(rcu_par_gp_wq, &rnp->rew.rew_work); + rnp->exp_need_flush = true; + } } /* Wait for workqueue jobs (if any) to complete. */ -- 2.17.1
