From 9f08cf088676c12a5b53bd5a29cf04f00c787b5d Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Tue, 8 Oct 2019 13:01:40 +0800 Subject: rcu: Avoid modifying mask_ofl_ipi in sync_rcu_exp_select_node_cpus() The "mask_ofl_ipi" is used to track which CPUs get IPIed, however in the IPI sending loop, "mask_ofl_ipi" along with another variable "mask_ofl_test" might also get modified to record which CPUs' quiesent states must be reported by the sync_rcu_exp_select_node_cpus() at the end of sync_rcu_exp_select_node_cpus(). This overlap of roles can be confusing, so this patch cleans things a little by using "mask_ofl_ipi" solely for determining which CPUs must be IPIed and "mask_ofl_test" for solely determining on behalf of which CPUs sync_rcu_exp_select_node_cpus() must report a quiscent state. Signed-off-by: Boqun Feng Signed-off-by: Paul E. McKenney Reviewed-by: Joel Fernandes (Google) Acked-by: Marco Elver --- kernel/rcu/tree_exp.h | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) (limited to 'kernel/rcu/tree_exp.h') diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 69c5aa64fcfd..6a6f328a5f52 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -387,10 +387,10 @@ retry_ipi: } ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); put_cpu(); - if (!ret) { - mask_ofl_ipi &= ~mask; + /* The CPU will report the QS in response to the IPI. */ + if (!ret) continue; - } + /* Failed, raced with CPU hotplug operation. */ raw_spin_lock_irqsave_rcu_node(rnp, flags); if ((rnp->qsmaskinitnext & mask) && @@ -401,13 +401,12 @@ retry_ipi: schedule_timeout_uninterruptible(1); goto retry_ipi; } - /* CPU really is offline, so we can ignore it. */ - if (!(rnp->expmask & mask)) - mask_ofl_ipi &= ~mask; + /* CPU really is offline, so we must report its QS. */ + if (rnp->expmask & mask) + mask_ofl_test |= mask; raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } /* Report quiescent states for those that went offline. */ - mask_ofl_test |= mask_ofl_ipi; if (mask_ofl_test) rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false); } -- cgit