From b474baf9f7c79f0233f511e816bde850d5d4c520 Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: Mon, 8 Nov 2021 16:18:57 -0800
Subject: [PATCH] rcu_tasks: Convert bespoke callback list to rcu_segcblist
structure
References: bnc#1189998 (PREEMPT_RT prerequisite backports)
Patch-mainline: v5.17-rc0
Git-commit: 9b073de1c7a354af7cb7100952599dde461aee45
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: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
kernel/rcu/Kconfig | 2 +-
kernel/rcu/tasks.h | 52 +++++++++++++++++++++++++++++-----------------------
2 files changed, 30 insertions(+), 24 deletions(-)
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index 4005f2728f1a..bf8e341e75b4 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -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"
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 6098e407290e..e2f13155cb1e 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -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