Commit 9b073de1 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu_tasks: Convert bespoke callback list to rcu_segcblist structure 



This commit moves from a bespoke head and tail pointer in the
rcu_tasks_percpu structure to an rcu_segcblist structure, thus allowing
associating the grace-period sequence number with groups of callbacks.
This in turn will allow callbacks to be invoked independently on
different CPUs.

Reported-by: default avatarMartin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent b14fb4fb

kernel/rcu/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -112,7 +112,7 @@ config RCU_STALL_COMMON 
	  making these warnings mandatory for the tree variants.



config RCU_NEED_SEGCBLIST

	def_bool ( TREE_RCU || TREE_SRCU )

	def_bool ( TREE_RCU || TREE_SRCU || TASKS_RCU_GENERIC )



config RCU_FANOUT

	int "Tree-based hierarchical RCU fanout value"

kernel/rcu/tasks.h

+29 −23
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
 */



#ifdef CONFIG_TASKS_RCU_GENERIC

#include "rcu_segcblist.h"



////////////////////////////////////////////////////////////////////////

//
@@ -21,13 +22,11 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp); 


/**

 * struct rcu_tasks_percpu - Per-CPU component of definition for a Tasks-RCU-like mechanism.

 * @cbs_head: Head of callback list.

 * @cbs_tail: Tail pointer for callback list.

 * @cblist: Callback list.

 * @cbs_pcpu_lock: Lock protecting per-CPU callback list.

 */

struct rcu_tasks_percpu {

	struct rcu_head *cbs_head;

	struct rcu_head **cbs_tail;

	struct rcu_segcblist cblist;

	raw_spinlock_t cbs_pcpu_lock;

};
@@ -180,8 +179,8 @@ static void cblist_init_generic(struct rcu_tasks *rtp) 
		if (cpu)

			raw_spin_lock_init(&rtpcp->cbs_pcpu_lock);

		raw_spin_lock(&rtpcp->cbs_pcpu_lock); // irqs already disabled.

		if (!WARN_ON_ONCE(rtpcp->cbs_tail))

			rtpcp->cbs_tail = &rtpcp->cbs_head;

		if (rcu_segcblist_empty(&rtpcp->cblist))

			rcu_segcblist_init(&rtpcp->cblist);

		raw_spin_unlock(&rtpcp->cbs_pcpu_lock); // irqs remain disabled.

	}

	raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
@@ -202,14 +201,13 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, 
	rtpcp = per_cpu_ptr(rtp->rtpcpu,

			    smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift));

	raw_spin_lock(&rtpcp->cbs_pcpu_lock);

	if (!rtpcp->cbs_tail) {

	if (!rcu_segcblist_is_enabled(&rtpcp->cblist)) {

		raw_spin_unlock(&rtpcp->cbs_pcpu_lock); // irqs remain disabled.

		cblist_init_generic(rtp);

		raw_spin_lock(&rtpcp->cbs_pcpu_lock); // irqs already disabled.

	}

	needwake = !rtpcp->cbs_head;

	WRITE_ONCE(*rtpcp->cbs_tail, rhp);

	rtpcp->cbs_tail = &rhp->next;

	needwake = rcu_segcblist_empty(&rtpcp->cblist);

	rcu_segcblist_enqueue(&rtpcp->cblist, rhp);

	raw_spin_unlock_irqrestore(&rtpcp->cbs_pcpu_lock, flags);

	/* We can't create the thread unless interrupts are enabled. */

	if (needwake && READ_ONCE(rtp->kthread_ptr))
@@ -231,8 +229,9 @@ static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp) 
static int __noreturn rcu_tasks_kthread(void *arg)

{

	unsigned long flags;

	struct rcu_head *list;

	struct rcu_head *next;

	int len;

	struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);

	struct rcu_head *rhp;

	struct rcu_tasks *rtp = arg;



	/* Run on housekeeping CPUs by default.  Sysadm can move if desired. */
@@ -253,16 +252,15 @@ static int __noreturn rcu_tasks_kthread(void *arg) 
		/* Pick up any new callbacks. */

		raw_spin_lock_irqsave(&rtpcp->cbs_pcpu_lock, flags);

		smp_mb__after_spinlock(); // Order updates vs. GP.

		list = rtpcp->cbs_head;

		rtpcp->cbs_head = NULL;

		rtpcp->cbs_tail = &rtpcp->cbs_head;

		rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));

		(void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq));

		raw_spin_unlock_irqrestore(&rtpcp->cbs_pcpu_lock, flags);



		/* If there were none, wait a bit and start over. */

		if (!list) {

		if (!rcu_segcblist_pend_cbs(&rtpcp->cblist)) {

			wait_event_interruptible(rtp->cbs_wq,

						 READ_ONCE(rtpcp->cbs_head));

			if (!rtpcp->cbs_head) {

						 rcu_segcblist_pend_cbs(&rtpcp->cblist));

			if (!rcu_segcblist_pend_cbs(&rtpcp->cblist)) {

				WARN_ON(signal_pending(current));

				set_tasks_gp_state(rtp, RTGS_WAIT_WAIT_CBS);

				schedule_timeout_idle(HZ/10);
@@ -279,14 +277,22 @@ static int __noreturn rcu_tasks_kthread(void *arg) 


		/* Invoke the callbacks. */

		set_tasks_gp_state(rtp, RTGS_INVOKE_CBS);

		while (list) {

			next = list->next;

		raw_spin_lock_irqsave(&rtpcp->cbs_pcpu_lock, flags);

		smp_mb__after_spinlock(); // Order updates vs. GP.

		rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));

		rcu_segcblist_extract_done_cbs(&rtpcp->cblist, &rcl);

		raw_spin_unlock_irqrestore(&rtpcp->cbs_pcpu_lock, flags);

		len = rcl.len;

		for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) {

			local_bh_disable();

			list->func(list);

			rhp->func(rhp);

			local_bh_enable();

			list = next;

			cond_resched();

		}

		raw_spin_lock_irqsave(&rtpcp->cbs_pcpu_lock, flags);

		rcu_segcblist_add_len(&rtpcp->cblist, -len);

		(void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq));

		raw_spin_unlock_irqrestore(&rtpcp->cbs_pcpu_lock, flags);

		/* Paranoid sleep to keep this from entering a tight loop */

		schedule_timeout_idle(rtp->gp_sleep);

	}
@@ -339,7 +345,7 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s) 
		data_race(rcu_seq_current(&rtp->tasks_gp_seq)),

		data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),

		".k"[!!data_race(rtp->kthread_ptr)],

		".C"[!!data_race(rtpcp->cbs_head)],

		".C"[!data_race(rcu_segcblist_empty(&rtpcp->cblist))],

		s);

}

#endif // #ifndef CONFIG_TINY_RCU