Commit 9f08cf08 authored Oct 08, 2019 by Boqun Feng Committed by Paul E. McKenney Dec 09, 2019

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 <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Acked-by: Marco Elver <elver@google.com>

parent 15c7c972

kernel/rcu/tree_exp.h

+6 −7

Original line number	Diff line number	Diff line
		@@ -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);
		}

Admin message