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Commit 2655d57e authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: prevent call_rcu() from diving into rcu core if irqs disabled 



This commit marks a first step towards making call_rcu() have
real-time behavior.  If irqs are disabled, don't dive into the
RCU core.  Later on, this new early exit will wake up the
per-CPU kthread, which first must be modified to handle the
cases involving callback storms.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent baa1ae0c

kernel/rcutree.c

+8 −1
Original line number Diff line number Diff line
@@ -1839,6 +1839,13 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), 
	/* Add the callback to our list. */

	*rdp->nxttail[RCU_NEXT_TAIL] = head;

	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;

	rdp->qlen++;



	/* If interrupts were disabled, don't dive into RCU core. */

	if (irqs_disabled_flags(flags)) {

		local_irq_restore(flags);

		return;

	}



	/*

	 * Force the grace period if too many callbacks or too long waiting.
@@ -1847,7 +1854,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), 
	 * invoking force_quiescent_state() if the newly enqueued callback

	 * is the only one waiting for a grace period to complete.

	 */

	if (unlikely(++rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {

	if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {



		/* Are we ignoring a completed grace period? */

		rcu_process_gp_end(rsp, rdp);