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Commit 38d30b33 authored by Paul E. McKenney's avatar Paul E. McKenney
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rcu: Adjust FQS offline checks for exact online-CPU detection 



Commit 7ec99de3 ("rcu: Provide exact CPU-online tracking for RCU"),
as its title suggests, got rid of RCU's remaining CPU-hotplug timing
guesswork.  This commit therefore removes the one-jiffy kludge that was
used to paper over this guesswork.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 3a19b46a

kernel/rcu/tree.c

+2 −15
Original line number Diff line number Diff line
@@ -1276,21 +1276,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, 
		return 1;

	}



	/*

	 * Check for the CPU being offline, but only if the grace period

	 * is old enough.  We don't need to worry about the CPU changing

	 * state: If we see it offline even once, it has been through a

	 * quiescent state.

	 *

	 * The reason for insisting that the grace period be at least

	 * one jiffy old is that CPUs that are not quite online and that

	 * have just gone offline can still execute RCU read-side critical

	 * sections.

	 */

	if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))

		return 0;  /* Grace period is not old enough. */

	barrier();

	if (cpu_is_offline(rdp->cpu)) {

	/* Check for the CPU being offline. */

	if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp))) {

		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));

		rdp->offline_fqs++;

		return 1;