From: Boqun Feng Date: Fri, 15 Jun 2018 19:06:31 +0000 (-0700) Subject: rcu: Make expedited GPs handle CPU 0 being offline X-Git-Tag: v4.19-rc1~214^2^2~90 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=fcc63543650150629c8a873cbef3578770acecd9;p=linux.git rcu: Make expedited GPs handle CPU 0 being offline 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 queues the work on WORK_CPU_UNBOUND if there are no online CPUs corresponding to 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(). Signed-off-by: Boqun Feng [ paulmck: Disable preemption to close offline race window. ] Signed-off-by: Paul E. McKenney [ paulmck: Apply Peter Zijlstra feedback on CPU selection. ] Tested-by: Aneesh Kumar K.V --- diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index c6385ee1af65..b3df3b770afb 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")); @@ -493,7 +494,13 @@ 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); + preempt_disable(); + cpu = cpumask_next(rnp->grplo - 1, cpu_online_mask); + /* If all offline, queue the work on an unbound CPU. */ + if (unlikely(cpu > rnp->grphi)) + cpu = WORK_CPU_UNBOUND; + queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work); + preempt_enable(); rnp->exp_need_flush = true; }