[PATCH rcu 17/32] rcu-tasks: Add data structures for lightweight grace periods

["Paul E. McKenney" <paulmck@kernel.org>]

This commit adds fields to task_struct and to rcu_tasks_percpu that will
be used to avoid the task-list scan for RCU Tasks Trace grace periods,
and also initializes these fields.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: KP Singh <kpsingh@kernel.org>
---
 include/linux/sched.h | 2 ++
 init/init_task.c      | 1 +
 kernel/fork.c         | 1 +
 kernel/rcu/tasks.h    | 4 ++++
 4 files changed, 8 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e6eb5871593e9..b88caf54e1686 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -844,6 +844,8 @@ struct task_struct {
 	int				trc_ipi_to_cpu;
 	union rcu_special		trc_reader_special;
 	struct list_head		trc_holdout_list;
+	struct list_head		trc_blkd_node;
+	int				trc_blkd_cpu;
 #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
 
 	struct sched_info		sched_info;
diff --git a/init/init_task.c b/init/init_task.c
index 73cc8f03511a3..ff6c4b9bfe6b1 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -157,6 +157,7 @@ struct task_struct init_task
 	.trc_reader_nesting = 0,
 	.trc_reader_special.s = 0,
 	.trc_holdout_list = LIST_HEAD_INIT(init_task.trc_holdout_list),
+	.trc_blkd_node = LIST_HEAD_INIT(init_task.trc_blkd_node),
 #endif
 #ifdef CONFIG_CPUSETS
 	.mems_allowed_seq = SEQCNT_SPINLOCK_ZERO(init_task.mems_allowed_seq,
diff --git a/kernel/fork.c b/kernel/fork.c
index 9d44f2d46c696..1950eb8702441 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1814,6 +1814,7 @@ static inline void rcu_copy_process(struct task_struct *p)
 	p->trc_reader_nesting = 0;
 	p->trc_reader_special.s = 0;
 	INIT_LIST_HEAD(&p->trc_holdout_list);
+	INIT_LIST_HEAD(&p->trc_blkd_node);
 #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
 }
 
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 64eb4d7b142e3..fd4508af055e6 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -29,6 +29,7 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
  * @rtp_work: Work queue for invoking callbacks.
  * @rtp_irq_work: IRQ work queue for deferred wakeups.
  * @barrier_q_head: RCU callback for barrier operation.
+ * @rtp_blkd_tasks: List of tasks blocked as readers.
  * @cpu: CPU number corresponding to this entry.
  * @rtpp: Pointer to the rcu_tasks structure.
  */
@@ -40,6 +41,7 @@ struct rcu_tasks_percpu {
 	struct work_struct rtp_work;
 	struct irq_work rtp_irq_work;
 	struct rcu_head barrier_q_head;
+	struct list_head rtp_blkd_tasks;
 	int cpu;
 	struct rcu_tasks *rtpp;
 };
@@ -256,6 +258,8 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
 		INIT_WORK(&rtpcp->rtp_work, rcu_tasks_invoke_cbs_wq);
 		rtpcp->cpu = cpu;
 		rtpcp->rtpp = rtp;
+		if (!rtpcp->rtp_blkd_tasks.next)
+			INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks);
 		raw_spin_unlock_rcu_node(rtpcp); // irqs remain disabled.
 	}
 	raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
-- 
2.31.1.189.g2e36527f23