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Commit c9a24e2d authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Make quiescent-state reporting use ->gp_seq 



This commit switches the functions reporting quiescent states from
use of ->gpnum to ->gp_seq.  In either case, the point is to handle
races where a given grace period ends before a quiescent state can
be reported.  Failing to catch these races would result in too-short
grace periods, hence the checking.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 78c5a67f

kernel/rcu/tree.c

+9 −9
Original line number Diff line number Diff line
@@ -2242,7 +2242,7 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) 
 * must be represented by the same rcu_node structure (which need not be a

 * leaf rcu_node structure, though it often will be).  The gps parameter

 * is the grace-period snapshot, which means that the quiescent states

 * are valid only if rnp->gpnum is equal to gps.  That structure's lock

 * are valid only if rnp->gp_seq is equal to gps.  That structure's lock

 * must be held upon entry, and it is released before return.

 */

static void
@@ -2257,7 +2257,7 @@ rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp, 


	/* Walk up the rcu_node hierarchy. */

	for (;;) {

		if (!(rnp->qsmask & mask) || rnp->gpnum != gps) {

		if (!(rnp->qsmask & mask) || rnp->gp_seq != gps) {



			/*

			 * Our bit has already been cleared, or the
@@ -2335,8 +2335,8 @@ static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp, 
		return;

	}



	/* Report up the rest of the hierarchy, tracking current ->gpnum. */

	gps = rnp->gpnum;

	/* Report up the rest of the hierarchy, tracking current ->gp_seq. */

	gps = rnp->gp_seq;

	mask = rnp->grpmask;

	raw_spin_unlock_rcu_node(rnp);	/* irqs remain disabled. */

	raw_spin_lock_rcu_node(rnp_p);	/* irqs already disabled. */
@@ -2357,8 +2357,8 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp) 


	rnp = rdp->mynode;

	raw_spin_lock_irqsave_rcu_node(rnp, flags);

	if (rdp->cpu_no_qs.b.norm || rdp->gpnum != rnp->gpnum ||

	    rnp->completed == rnp->gpnum || rdp->gpwrap) {

	if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||

	    rdp->gpwrap) {



		/*

		 * The grace period in which this quiescent state was
@@ -2383,7 +2383,7 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp) 
		 */

		needwake = rcu_accelerate_cbs(rsp, rnp, rdp);



		rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);

		rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);

		/* ^^^ Released rnp->lock */

		if (needwake)

			rcu_gp_kthread_wake(rsp);
@@ -2688,8 +2688,8 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp)) 
			}

		}

		if (mask != 0) {

			/* Idle/offline CPUs, report (releases rnp->lock. */

			rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);

			/* Idle/offline CPUs, report (releases rnp->lock). */

			rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);

		} else {

			/* Nothing to do here, so just drop the lock. */

			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);