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Commit 07079d53 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
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rcu: Prohibit starting new grace periods while forcing quiescent states 



Reduce the number and variety of race conditions by prohibiting
the start of a new grace period while force_quiescent_state() is
active. A new fqs_active flag in the rcu_state structure is used
to trace whether or not force_quiescent_state() is active, and
this new flag is tested by rcu_start_gp().  If the CPU that
closed out the last grace period needs another grace period,
this new grace period may be delayed up to one scheduling-clock
tick, but it will eventually get started.

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: <126264655052-git-send-email->
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 559569ac

kernel/rcutree.c

+17 −14
Original line number Diff line number Diff line
@@ -659,7 +659,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) 
	struct rcu_data *rdp = rsp->rda[smp_processor_id()];

	struct rcu_node *rnp = rcu_get_root(rsp);



	if (!cpu_needs_another_gp(rsp, rdp)) {

	if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) {

		if (rnp->completed == rsp->completed) {

			spin_unlock_irqrestore(&rnp->lock, flags);

			return;
@@ -1195,6 +1195,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) 
	struct rcu_node *rnp = rcu_get_root(rsp);

	u8 signaled;

	u8 forcenow;

	u8 gpdone;



	if (!rcu_gp_in_progress(rsp))

		return;  /* No grace period in progress, nothing to force. */
@@ -1206,15 +1207,16 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) 
	    (long)(rsp->jiffies_force_qs - jiffies) >= 0)

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

	rsp->n_force_qs++;

	spin_lock(&rnp->lock);

	spin_lock(&rnp->lock);  /* irqs already disabled */

	lastcomp = rsp->gpnum - 1;

	signaled = rsp->signaled;

	rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;

	if(!rcu_gp_in_progress(rsp)) {

		rsp->n_force_qs_ngp++;

		spin_unlock(&rnp->lock);

		spin_unlock(&rnp->lock);  /* irqs remain disabled */

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

	}

	rsp->fqs_active = 1;

	switch (signaled) {

	case RCU_GP_IDLE:

	case RCU_GP_INIT:
@@ -1223,15 +1225,16 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) 


	case RCU_SAVE_DYNTICK:



		spin_unlock(&rnp->lock);

		spin_unlock(&rnp->lock);  /* irqs remain disabled */

		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_fqs_ret;

		spin_lock(&rnp->lock);

		gpdone = rcu_process_dyntick(rsp, lastcomp,

					     dyntick_save_progress_counter);

		spin_lock(&rnp->lock);  /* irqs already disabled */

		if (gpdone)

			break;

		/* fall into next case. */



	case RCU_SAVE_COMPLETED:
@@ -1252,17 +1255,17 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) 
	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_fqs_ret;

		spin_unlock(&rnp->lock);  /* irqs remain disabled */

		gpdone = rcu_process_dyntick(rsp, rsp->completed_fqs,

					     rcu_implicit_dynticks_qs);



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



		spin_lock(&rnp->lock);

		spin_lock(&rnp->lock);  /* irqs already disabled */

		break;

	}

	spin_unlock(&rnp->lock);

	rsp->fqs_active = 0;

	spin_unlock(&rnp->lock);  /* irqs remain disabled */

unlock_fqs_ret:

	spin_unlock_irqrestore(&rsp->fqslock, flags);

}

kernel/rcutree.h

+2 −0
Original line number Diff line number Diff line
@@ -277,6 +277,8 @@ struct rcu_state { 


	u8	signaled ____cacheline_internodealigned_in_smp;

						/* Force QS state. */

	u8	fqs_active;			/* force_quiescent_state() */

						/*  is running. */

	long	gpnum;				/* Current gp number. */

	long	completed;			/* # of last completed gp. */