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Commit b0e165c0 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
Browse files

rcu: Add debug checks to TREE_PREEMPT_RCU for premature grace periods 



Check to make sure that there are no blocked tasks for the previous
grace period while initializing for the next grace period, verify
that rcu_preempt_qs() is given the correct CPU number and is never
called for an offline CPU.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
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
LKML-Reference: <12528585111986-git-send-email->
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent bbe3eae8

kernel/rcutree.c

+2 −0
Original line number Diff line number Diff line
@@ -632,6 +632,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) 
	/* Special-case the common single-level case. */

	if (NUM_RCU_NODES == 1) {

		rnp->qsmask = rnp->qsmaskinit;

		rcu_preempt_check_blocked_tasks(rnp);

		rnp->gpnum = rsp->gpnum;

		rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */

		spin_unlock_irqrestore(&rnp->lock, flags);
@@ -665,6 +666,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) 
	for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) {

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

		rnp_cur->qsmask = rnp_cur->qsmaskinit;

		rcu_preempt_check_blocked_tasks(rnp);

		rnp->gpnum = rsp->gpnum;

		spin_unlock(&rnp_cur->lock);	/* irqs already disabled. */

	}

kernel/rcutree_plugin.h

+25 −0
Original line number Diff line number Diff line
@@ -86,6 +86,7 @@ static void rcu_preempt_qs(int cpu) 


	if (t->rcu_read_lock_nesting &&

	    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {

		WARN_ON_ONCE(cpu != smp_processor_id());



		/* Possibly blocking in an RCU read-side critical section. */

		rdp = rcu_preempt_state.rda[cpu];
@@ -103,7 +104,11 @@ static void rcu_preempt_qs(int cpu) 
		 * state for the current grace period), then as long

		 * as that task remains queued, the current grace period

		 * cannot end.

		 *

		 * But first, note that the current CPU must still be

		 * on line!

		 */

		WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);

		phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1);

		list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);

		smp_mb();  /* Ensure later ctxt swtch seen after above. */
@@ -258,6 +263,18 @@ static void rcu_print_task_stall(struct rcu_node *rnp) 


#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */



/*

 * Check that the list of blocked tasks for the newly completed grace

 * period is in fact empty.  It is a serious bug to complete a grace

 * period that still has RCU readers blocked!  This function must be

 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock

 * must be held by the caller.

 */

static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)

{

	WARN_ON_ONCE(!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]));

}



/*

 * Check for preempted RCU readers for the specified rcu_node structure.

 * If the caller needs a reliable answer, it must hold the rcu_node's
@@ -450,6 +467,14 @@ static void rcu_print_task_stall(struct rcu_node *rnp) 


#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */



/*

 * Because there is no preemptable RCU, there can be no readers blocked,

 * so there is no need to check for blocked tasks.

 */

static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)

{

}



/*

 * Because preemptable RCU does not exist, there are never any preempted

 * RCU readers.