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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 <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>
This commit is contained in:
Boqun Feng 2018-06-15 12:06:31 -07:00 committed by Paul E. McKenney
parent 5257514d88
commit fcc6354365
1 changed files with 8 additions and 1 deletions
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9
kernel/rcu/tree_exp.h
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@ -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;
}