[PATCH rcu 04/32] rcu-tasks: Drive synchronous grace periods from calling task

Paul E. McKenney
2022-06-20T22:54:28Z

This commit causes synchronous grace periods to be driven from the task
invoking synchronize_rcu_*(), allowing these functions to be invoked from
the mid-boot dead zone extending from when the scheduler was initialized
to to point that the various RCU tasks grace-period kthreads are spawned.
This change will allow the self-tests to run in a consistent manner.

Reported-by: Matthew Wilcox <willy@infradead.org>
Reported-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tasks.h | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index ad993c4ed924f..bd9f2e24f5c73 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -495,17 +495,21 @@ static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp)
}

// Wait for one grace period.
-static void rcu_tasks_one_gp(struct rcu_tasks *rtp)
+static void rcu_tasks_one_gp(struct rcu_tasks *rtp, bool midboot)
{
int needgpcb;

mutex_lock(&rtp->tasks_gp_mutex);
- set_tasks_gp_state(rtp, RTGS_WAIT_CBS);

// If there were none, wait a bit and start over.
- rcuwait_wait_event(&rtp->cbs_wait,
- (needgpcb = rcu_tasks_need_gpcb(rtp)),
- TASK_IDLE);
+ if (unlikely(midboot)) {
+ needgpcb = 0x2;
+ } else {
+ set_tasks_gp_state(rtp, RTGS_WAIT_CBS);
+ rcuwait_wait_event(&rtp->cbs_wait,
+ (needgpcb = rcu_tasks_need_gpcb(rtp)),
+ TASK_IDLE);
+ }

if (needgpcb & 0x2) {
// Wait for one grace period.
@@ -540,7 +544,7 @@ static int __noreturn rcu_tasks_kthread(void *arg)
for (;;) {
// Wait for one grace period and invoke any callbacks
// that are ready.
- rcu_tasks_one_gp(rtp);
+ rcu_tasks_one_gp(rtp, false);

// Paranoid sleep to keep this from entering a tight loop.
schedule_timeout_idle(rtp->gp_sleep);
@@ -554,8 +558,12 @@ static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp)
RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
"synchronize_rcu_tasks called too soon");

- /* Wait for the grace period. */
- wait_rcu_gp(rtp->call_func);
+ // If the grace-period kthread is running, use it.
+ if (READ_ONCE(rtp->kthread_ptr)) {
+ wait_rcu_gp(rtp->call_func);
+ return;
+ }
+ rcu_tasks_one_gp(rtp, true);
}

/* Spawn RCU-tasks grace-period kthread. */
--
2.31.1.189.g2e36527f23