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Commit b9a425cf authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Pull out wait_event*() condition into helper function 



The condition for the wait_event_interruptible_timeout() that waits
to do the next force-quiescent-state scan is a bit ornate:

	((gf = READ_ONCE(rsp->gp_flags)) &
	 RCU_GP_FLAG_FQS) ||
	(!READ_ONCE(rnp->qsmask) &&
	 !rcu_preempt_blocked_readers_cgp(rnp))

This commit therefore pulls this condition out into a helper function
and comments its component conditions.

Reported-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 99a930b0

kernel/rcu/tree.c

+21 −5
Original line number Diff line number Diff line
@@ -1903,6 +1903,26 @@ static int rcu_gp_init(struct rcu_state *rsp) 
	return 1;

}



/*

 * Helper function for wait_event_interruptible_timeout() wakeup

 * at force-quiescent-state time.

 */

static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)

{

	struct rcu_node *rnp = rcu_get_root(rsp);



	/* Someone like call_rcu() requested a force-quiescent-state scan. */

	*gfp = READ_ONCE(rsp->gp_flags);

	if (*gfp & RCU_GP_FLAG_FQS)

		return true;



	/* The current grace period has completed. */

	if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))

		return true;



	return false;

}



/*

 * Do one round of quiescent-state forcing.

 */
@@ -2067,11 +2087,7 @@ static int __noreturn rcu_gp_kthread(void *arg) 
					       TPS("fqswait"));

			rsp->gp_state = RCU_GP_WAIT_FQS;

			ret = wait_event_interruptible_timeout(rsp->gp_wq,

					((gf = READ_ONCE(rsp->gp_flags)) &

					 RCU_GP_FLAG_FQS) ||

					(!READ_ONCE(rnp->qsmask) &&

					 !rcu_preempt_blocked_readers_cgp(rnp)),

					j);

					rcu_gp_fqs_check_wake(rsp, &gf), j);

			rsp->gp_state = RCU_GP_DONE_FQS;

			/* Locking provides needed memory barriers. */

			/* If grace period done, leave loop. */