Commit a0b6c9a7 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
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rcu: Clean up code based on review feedback from Josh Triplett, part 4 



These issues identified during an old-fashioned face-to-face code
review extending over many hours.  This group improves an existing
abstraction and introduces two new ones.  It also fixes an RCU
stall-warning bug found while making the other changes.

o	Make RCU_INIT_FLAVOR() declare its own variables, removing
	the need to declare them at each call site.

o	Create an rcu_for_each_leaf() macro that scans the leaf
	nodes of the rcu_node tree.

o	Create an rcu_for_each_node_breadth_first() macro that does
	a breadth-first traversal of the rcu_node tree, AKA
	stepping through the array in index-number order.

o	If all CPUs corresponding to a given leaf rcu_node
	structure go offline, then any tasks queued on that leaf
	will be moved to the root rcu_node structure.  Therefore,
	the stall-warning code must dump out tasks queued on the
	root rcu_node structure as well as those queued on the leaf
	rcu_node structures.

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
Cc: dhowells@redhat.com
LKML-Reference: <12541491934126-git-send-email->
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 3d76c082

kernel/rcutree.c

+28 −25
Original line number Diff line number Diff line
@@ -462,8 +462,6 @@ static void print_other_cpu_stall(struct rcu_state *rsp) 
	long delta;

	unsigned long flags;

	struct rcu_node *rnp = rcu_get_root(rsp);

	struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];

	struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];



	/* Only let one CPU complain about others per time interval. */
@@ -474,18 +472,24 @@ static void print_other_cpu_stall(struct rcu_state *rsp) 
		return;

	}

	rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;



	/*

	 * Now rat on any tasks that got kicked up to the root rcu_node

	 * due to CPU offlining.

	 */

	rcu_print_task_stall(rnp);

	spin_unlock_irqrestore(&rnp->lock, flags);



	/* OK, time to rat on our buddy... */



	printk(KERN_ERR "INFO: RCU detected CPU stalls:");

	for (; rnp_cur < rnp_end; rnp_cur++) {

	rcu_for_each_leaf_node(rsp, rnp) {

		rcu_print_task_stall(rnp);

		if (rnp_cur->qsmask == 0)

		if (rnp->qsmask == 0)

			continue;

		for (cpu = 0; cpu <= rnp_cur->grphi - rnp_cur->grplo; cpu++)

			if (rnp_cur->qsmask & (1UL << cpu))

				printk(" %d", rnp_cur->grplo + cpu);

		for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)

			if (rnp->qsmask & (1UL << cpu))

				printk(" %d", rnp->grplo + cpu);

	}

	printk(" (detected by %d, t=%ld jiffies)\n",

	       smp_processor_id(), (long)(jiffies - rsp->gp_start));
@@ -649,7 +653,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) 
	 * one corresponding to this CPU, due to the fact that we have

	 * irqs disabled.

	 */

	for (rnp = &rsp->node[0]; rnp < &rsp->node[NUM_RCU_NODES]; rnp++) {

	rcu_for_each_node_breadth_first(rsp, rnp) {

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

		rcu_preempt_check_blocked_tasks(rnp);

		rnp->qsmask = rnp->qsmaskinit;
@@ -1042,33 +1046,32 @@ static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp, 
	int cpu;

	unsigned long flags;

	unsigned long mask;

	struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];

	struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];

	struct rcu_node *rnp;



	for (; rnp_cur < rnp_end; rnp_cur++) {

	rcu_for_each_leaf_node(rsp, rnp) {

		mask = 0;

		spin_lock_irqsave(&rnp_cur->lock, flags);

		spin_lock_irqsave(&rnp->lock, flags);

		if (rsp->completed != lastcomp) {

			spin_unlock_irqrestore(&rnp_cur->lock, flags);

			spin_unlock_irqrestore(&rnp->lock, flags);

			return 1;

		}

		if (rnp_cur->qsmask == 0) {

			spin_unlock_irqrestore(&rnp_cur->lock, flags);

		if (rnp->qsmask == 0) {

			spin_unlock_irqrestore(&rnp->lock, flags);

			continue;

		}

		cpu = rnp_cur->grplo;

		cpu = rnp->grplo;

		bit = 1;

		for (; cpu <= rnp_cur->grphi; cpu++, bit <<= 1) {

			if ((rnp_cur->qsmask & bit) != 0 && f(rsp->rda[cpu]))

		for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {

			if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))

				mask |= bit;

		}

		if (mask != 0 && rsp->completed == lastcomp) {



			/* cpu_quiet_msk() releases rnp_cur->lock. */

			cpu_quiet_msk(mask, rsp, rnp_cur, flags);

			/* cpu_quiet_msk() releases rnp->lock. */

			cpu_quiet_msk(mask, rsp, rnp, flags);

			continue;

		}

		spin_unlock_irqrestore(&rnp_cur->lock, flags);

		spin_unlock_irqrestore(&rnp->lock, flags);

	}

	return 0;

}
@@ -1550,6 +1553,10 @@ static void __init rcu_init_one(struct rcu_state *rsp) 
 */

#define RCU_INIT_FLAVOR(rsp, rcu_data) \

do { \

	int i; \

	int j; \

	struct rcu_node *rnp; \

	\

	rcu_init_one(rsp); \

	rnp = (rsp)->level[NUM_RCU_LVLS - 1]; \

	j = 0; \
@@ -1564,10 +1571,6 @@ do { \ 


void __init __rcu_init(void)

{

	int i;			/* All used by RCU_INIT_FLAVOR(). */

	int j;

	struct rcu_node *rnp;



	rcu_bootup_announce();

#ifdef CONFIG_RCU_CPU_STALL_DETECTOR

	printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n");

kernel/rcutree.h

+12 −0
Original line number Diff line number Diff line
@@ -106,6 +106,18 @@ struct rcu_node { 
				/*  blocked_tasks[] array. */

} ____cacheline_internodealigned_in_smp;



/*

 * Do a full breadth-first scan of the rcu_node structures for the

 * specified rcu_state structure.

 */

#define rcu_for_each_node_breadth_first(rsp, rnp) \

	for ((rnp) = &(rsp)->node[0]; \

	     (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)



#define rcu_for_each_leaf_node(rsp, rnp) \

	for ((rnp) = (rsp)->level[NUM_RCU_LVLS - 1]; \

	     (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)



/* Index values for nxttail array in struct rcu_data. */

#define RCU_DONE_TAIL		0	/* Also RCU_WAIT head. */

#define RCU_WAIT_TAIL		1	/* Also RCU_NEXT_READY head. */

kernel/rcutree_plugin.h

+0 −4
Original line number Diff line number Diff line
@@ -423,10 +423,6 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu) 
 */

static void __init __rcu_init_preempt(void)

{

	int i;			/* All used by RCU_INIT_FLAVOR(). */

	int j;

	struct rcu_node *rnp;



	RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data);

}

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