4.18-stable review patch. If anyone has any objections, please let me know.
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From: Boqun Feng boqun.feng@gmail.com
commit fcc63543650150629c8a873cbef3578770acecd9 upstream.
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 boqun.feng@gmail.com [ paulmck: Disable preemption to close offline race window. ] Signed-off-by: Paul E. McKenney paulmck@linux.vnet.ibm.com [ paulmck: Apply Peter Zijlstra feedback on CPU selection. ] Tested-by: Aneesh Kumar K.V aneesh.kumar@linux.vnet.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/rcu/tree_exp.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
--- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -472,6 +472,7 @@ retry_ipi: 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")); @@ -492,7 +493,13 @@ static void sync_rcu_exp_select_cpus(str 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; }