rcu: Move grace-period pre-init delay after pre-init (f34f2f58) · Commits · 戴 / test

The main race with the early part of grace-period initialization appears to be with CPU hotplug. To more fully open this race window, this commit moves the rcu_gp_slow() from the beginning of the early initialization loop to follow that loop, thus widening the race window, especially for the rcu_node structures that are initialized last. This commit also expands rcutree.gp_preinit_delay from 3 to 12, giving the same overall delay in the grace period, but concentrated in the spot where it will do the most good. Signed-off-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1900,7 +1900,6 @@ static bool rcu_gp_init(struct rcu_state *rsp)
		* will handle subsequent offline CPUs.
		*/
		rcu_for_each_leaf_node(rsp, rnp) {
		rcu_gp_slow(rsp, gp_preinit_delay);
		spin_lock(&rsp->ofl_lock);
		raw_spin_lock_irq_rcu_node(rnp);
		if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
		@@ -1945,6 +1944,7 @@ static bool rcu_gp_init(struct rcu_state *rsp)
		raw_spin_unlock_irq_rcu_node(rnp);
		spin_unlock(&rsp->ofl_lock);
		}
		rcu_gp_slow(rsp, gp_preinit_delay); /* Races with CPU hotplug. */

		/*
		* Set the quiescent-state-needed bits in all the rcu_node

tools/testing/selftests/rcutorture/configs/rcu/TREE03.boot

+1 −1

Original line number	Diff line number	Diff line
		rcutorture.onoff_interval=1 rcutorture.onoff_holdoff=30
		rcutree.gp_preinit_delay=3
		rcutree.gp_preinit_delay=12
		rcutree.gp_init_delay=3
		rcutree.gp_cleanup_delay=3
		rcutree.kthread_prio=2

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