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Commit f96e9232 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
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rcu: Adjust force_quiescent_state() locking, step 1 



This causes rnp->lock to be held on entry to
force_quiescent_state()'s switch statement.  This is a first
step towards prohibiting starting grace periods while
force_quiescent_state() is executing, which will reduce the
number and complexity of races that force_quiescent_state() is
involved in.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12626465501455-git-send-email->
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 7284ce6c

kernel/rcutree.c

+18 −9
Original line number Diff line number Diff line
@@ -1204,7 +1204,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) 
	}

	if (relaxed &&

	    (long)(rsp->jiffies_force_qs - jiffies) >= 0)

		goto unlock_ret; /* no emergency and done recently. */

		goto unlock_fqs_ret; /* no emergency and done recently. */

	rsp->n_force_qs++;

	spin_lock(&rnp->lock);

	lastcomp = rsp->gpnum - 1;
@@ -1213,31 +1213,32 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) 
	if(!rcu_gp_in_progress(rsp)) {

		rsp->n_force_qs_ngp++;

		spin_unlock(&rnp->lock);

		goto unlock_ret;  /* no GP in progress, time updated. */

		goto unlock_fqs_ret;  /* no GP in progress, time updated. */

	}

	spin_unlock(&rnp->lock);

	switch (signaled) {

	case RCU_GP_IDLE:

	case RCU_GP_INIT:



		spin_unlock(&rnp->lock);

		break; /* grace period idle or initializing, ignore. */



	case RCU_SAVE_DYNTICK:



		spin_unlock(&rnp->lock);

		if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)

			break; /* So gcc recognizes the dead code. */



		/* Record dyntick-idle state. */

		if (rcu_process_dyntick(rsp, lastcomp,

					dyntick_save_progress_counter))

			goto unlock_ret;

			goto unlock_fqs_ret;

		spin_lock(&rnp->lock);

		/* fall into next case. */



	case RCU_SAVE_COMPLETED:



		/* Update state, record completion counter. */

		forcenow = 0;

		spin_lock(&rnp->lock);

		if (lastcomp + 1 == rsp->gpnum &&

		    lastcomp == rsp->completed &&

		    rsp->signaled == signaled) {
@@ -1245,23 +1246,31 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) 
			rsp->completed_fqs = lastcomp;

			forcenow = signaled == RCU_SAVE_COMPLETED;

		}

		if (!forcenow) {

			spin_unlock(&rnp->lock);

		if (!forcenow)

			break;

		}

		/* fall into next case. */



	case RCU_FORCE_QS:



		/* Check dyntick-idle state, send IPI to laggarts. */

		spin_unlock(&rnp->lock);

		if (rcu_process_dyntick(rsp, rsp->completed_fqs,

					rcu_implicit_dynticks_qs))

			goto unlock_ret;

			goto unlock_fqs_ret;



		/* Leave state in case more forcing is required. */



		break;



	default:



		spin_unlock(&rnp->lock);

		WARN_ON_ONCE(1);

		break;

	}

unlock_ret:

unlock_fqs_ret:

	spin_unlock_irqrestore(&rsp->fqslock, flags);

}