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Date: Mon, 28 Sep 2015 10:14:37 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Petr Mladek <pmladek@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Josh Triplett <josh@...htriplett.org>,
Thomas Gleixner <tglx@...utronix.de>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>,
Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
Vlastimil Babka <vbabka@...e.cz>,
live-patching@...r.kernel.org, linux-api@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 17/18] rcu: Convert RCU gp kthreads into kthread worker
API
On Mon, Sep 21, 2015 at 03:03:58PM +0200, Petr Mladek wrote:
> Kthreads are currently implemented as an infinite loop. Each
> has its own variant of checks for terminating, freezing,
> awakening. In many cases it is unclear to say in which state
> it is and sometimes it is done a wrong way.
>
> The plan is to convert kthreads into kthread_worker or workqueues
> API. It allows to split the functionality into separate operations.
> It helps to make a better structure. Also it defines a clean state
> where no locks are taken, IRQs blocked, the kthread might sleep
> or even be safely migrated.
>
> The kthread worker API is useful when we want to have a dedicated
> single kthread for the work. It helps to make sure that it is
> available when needed. Also it allows a better control, e.g.
> define a scheduling priority.
>
> This patch converts RCU gp threads into the kthread worker API.
> They modify the scheduling, have their own logic to bind the process.
> They provide functions that are critical for the system to work
> and thus deserve a dedicated kthread.
>
> This patch tries to split start of the grace period and the quiescent
> state handling into separate works. The motivation is to avoid
> wait_events inside the work. Instead it queues the works when
> appropriate which is more typical for this API.
>
> On one hand, it should reduce spurious wakeups where the condition
> in the wait_event failed and the kthread went to sleep again.
>
> On the other hand, there is a small race window when the other
> work might get queued. We could detect and fix this situation
> at the beginning of the work but it is a bit ugly.
>
> The patch renames the functions kthread_wake() to kthread_worker_poke()
> that sounds more appropriate.
>
> Otherwise, the logic should stay the same. I did a lot of torturing
> and I did not see any problem with the current patch. But of course,
> it would deserve much more testing and reviewing before applying.
Suppose I later need to add helper kthreads to parallelize grace-period
initialization. How would I implement that in a freeze-friendly way?
Thanx, Paul
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> ---
> kernel/rcu/tree.c | 349 ++++++++++++++++++++++++++++++-----------------
> kernel/rcu/tree.h | 8 +-
> kernel/rcu/tree_plugin.h | 16 +--
> 3 files changed, 237 insertions(+), 136 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 08d1d3e63b9b..e115c3aee65d 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -482,7 +482,7 @@ void show_rcu_gp_kthreads(void)
>
> for_each_rcu_flavor(rsp) {
> pr_info("%s: wait state: %d ->state: %#lx\n",
> - rsp->name, rsp->gp_state, rsp->gp_kthread->state);
> + rsp->name, rsp->gp_state, rsp->gp_worker->task->state);
> /* sched_show_task(rsp->gp_kthread); */
> }
> }
> @@ -1179,7 +1179,7 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
> rsp->name, j - gpa,
> rsp->gpnum, rsp->completed,
> rsp->gp_flags, rsp->gp_state,
> - rsp->gp_kthread ? rsp->gp_kthread->state : 0);
> + rsp->gp_worker ? rsp->gp_worker->task->state : 0);
> }
>
> /*
> @@ -1577,19 +1577,66 @@ static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
> }
>
> /*
> - * Awaken the grace-period kthread for the specified flavor of RCU.
> - * Don't do a self-awaken, and don't bother awakening when there is
> - * nothing for the grace-period kthread to do (as in several CPUs
> - * raced to awaken, and we lost), and finally don't try to awaken
> - * a kthread that has not yet been created.
> + * Check if it makes sense to queue the kthread work that would
> + * start a new grace period.
> */
> -static void rcu_gp_kthread_wake(struct rcu_state *rsp)
> +static bool rcu_gp_start_ready(struct rcu_state *rsp)
> {
> - if (current == rsp->gp_kthread ||
> - !READ_ONCE(rsp->gp_flags) ||
> - !rsp->gp_kthread)
> + /* Someone like call_rcu() requested a new grace period. */
> + if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_INIT)
> + return true;
> +
> + return false;
> +
> +}
> +
> +/*
> + * Check if it makes sense to immediately queue the kthread work
> + * that would handle quiescent state.
> + *
> + * It does not check the timeout for forcing the quiescent state
> + * because the delayed kthread work should be scheduled at this
> + * time.
> + */
> +static bool rcu_gp_handle_qs_ready(struct rcu_state *rsp)
> +{
> + struct rcu_node *rnp = rcu_get_root(rsp);
> +
> + /* Someone like call_rcu() requested a force-quiescent-state scan. */
> + if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS)
> + return true;
> +
> + /* The current grace period has completed. */
> + if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
> + return true;
> +
> + return false;
> +}
> +
> +/*
> + * Poke the kthread worker that handles grace periods for the specified
> + * flavor of RCU. Return when there is nothing for the grace-period kthread
> + * worker to do (as in several CPUs raced to awaken, and we lost). Also
> + * don't try to use the kthread worker that has not been created yet.
> + * Finally, ignore requests from the kthread servicing the worker itself.
> + */
> +static void rcu_gp_kthread_worker_poke(struct rcu_state *rsp)
> +{
> + if (!READ_ONCE(rsp->gp_flags) ||
> + !rsp->gp_worker ||
> + rsp->gp_worker->task == current)
> return;
> - wake_up(&rsp->gp_wq);
> +
> + if (!rcu_gp_in_progress(rsp)) {
> + if (rcu_gp_start_ready(rsp))
> + queue_kthread_work(rsp->gp_worker, &rsp->gp_start_work);
> + return;
> + }
> +
> + if (rcu_gp_handle_qs_ready(rsp))
> + mod_delayed_kthread_work(rsp->gp_worker,
> + &rsp->gp_handle_qs_work,
> + 0);
> }
>
> /*
> @@ -1756,7 +1803,7 @@ static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
> static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
> {
> unsigned long flags;
> - bool needwake;
> + bool needpoke;
> struct rcu_node *rnp;
>
> local_irq_save(flags);
> @@ -1769,10 +1816,10 @@ static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
> return;
> }
> smp_mb__after_unlock_lock();
> - needwake = __note_gp_changes(rsp, rnp, rdp);
> + needpoke = __note_gp_changes(rsp, rnp, rdp);
> raw_spin_unlock_irqrestore(&rnp->lock, flags);
> - if (needwake)
> - rcu_gp_kthread_wake(rsp);
> + if (needpoke)
> + rcu_gp_kthread_worker_poke(rsp);
> }
>
> static void rcu_gp_slow(struct rcu_state *rsp, int delay)
> @@ -1905,25 +1952,6 @@ static int rcu_gp_init(struct rcu_state *rsp)
> }
>
> /*
> - * Helper function for wait_event_interruptible_timeout() wakeup
> - * at force-quiescent-state time.
> - */
> -static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp)
> -{
> - struct rcu_node *rnp = rcu_get_root(rsp);
> -
> - /* Someone like call_rcu() requested a force-quiescent-state scan. */
> - if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS)
> - return true;
> -
> - /* The current grace period has completed. */
> - if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
> - return true;
> -
> - return false;
> -}
> -
> -/*
> * Do one round of quiescent-state forcing.
> */
> static void rcu_gp_fqs(struct rcu_state *rsp)
> @@ -2067,94 +2095,157 @@ static unsigned long normalize_jiffies_till_next_fqs(void)
> }
>
> /*
> - * Body of kthread that handles grace periods.
> + * Initialize kthread worker for handling grace periods.
> */
> -static int __noreturn rcu_gp_kthread(void *arg)
> +static void rcu_gp_init_func(struct kthread_work *work)
> {
> - unsigned long timeout, j;
> - struct rcu_state *rsp = arg;
> - struct rcu_node *rnp = rcu_get_root(rsp);
> + struct rcu_state *rsp = container_of(work, struct rcu_state,
> + gp_init_work);
>
> rcu_bind_gp_kthread();
> - for (;;) {
>
> - /* Handle grace-period start. */
> - for (;;) {
> - trace_rcu_grace_period(rsp->name,
> - READ_ONCE(rsp->gpnum),
> - TPS("reqwait"));
> - rsp->gp_state = RCU_GP_WAIT_GPS;
> - wait_event_interruptible(rsp->gp_wq,
> - READ_ONCE(rsp->gp_flags) &
> - RCU_GP_FLAG_INIT);
> - rsp->gp_state = RCU_GP_DONE_GPS;
> - /* Locking provides needed memory barrier. */
> - if (rcu_gp_init(rsp))
> - break;
> - cond_resched_rcu_qs();
> - WRITE_ONCE(rsp->gp_activity, jiffies);
> - WARN_ON(signal_pending(current));
> - trace_rcu_grace_period(rsp->name,
> - READ_ONCE(rsp->gpnum),
> - TPS("reqwaitsig"));
> + trace_rcu_grace_period(rsp->name,
> + READ_ONCE(rsp->gpnum),
> + TPS("reqwait"));
> + rsp->gp_state = RCU_GP_WAIT_GPS;
> +}
> +
> +/*
> + * Function for RCU kthread work that starts a new grace period.
> + */
> +static void rcu_gp_start_func(struct kthread_work *work)
> +{
> + unsigned long timeout;
> + struct rcu_state *rsp = container_of(work, struct rcu_state,
> + gp_start_work);
> +
> + /*
> + * There is a small race window in rcu_gp_kthread_worker_poke().
> + * Check if the grace period has already started and the quiescent
> + * state should get handled instead.
> + */
> + if (rcu_gp_in_progress(rsp)) {
> + if (rcu_gp_handle_qs_ready(rsp)) {
> + mod_delayed_kthread_work(rsp->gp_worker,
> + &rsp->gp_handle_qs_work,
> + 0);
> }
> + return;
> + }
>
> + rsp->gp_state = RCU_GP_DONE_GPS;
> + if (rcu_gp_init(rsp)) {
> /* Handle quiescent-state forcing. */
> rsp->first_gp_fqs = true;
> timeout = normalize_jiffies_till_first_fqs();
> rsp->jiffies_force_qs = jiffies + timeout;
> - for (;;) {
> - trace_rcu_grace_period(rsp->name,
> - READ_ONCE(rsp->gpnum),
> - TPS("fqswait"));
> - rsp->gp_state = RCU_GP_WAIT_FQS;
> - wait_event_interruptible_timeout(rsp->gp_wq,
> - rcu_gp_fqs_check_wake(rsp),
> - timeout);
> - rsp->gp_state = RCU_GP_DOING_FQS;
> -try_again:
> - /* Locking provides needed memory barriers. */
> - /* If grace period done, leave loop. */
> - if (!READ_ONCE(rnp->qsmask) &&
> - !rcu_preempt_blocked_readers_cgp(rnp))
> - break;
> - /* If time for quiescent-state forcing, do it. */
> - if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
> - (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS)) {
> - trace_rcu_grace_period(rsp->name,
> - READ_ONCE(rsp->gpnum),
> - TPS("fqsstart"));
> - rcu_gp_fqs(rsp);
> - timeout = normalize_jiffies_till_next_fqs();
> - rsp->jiffies_force_qs = jiffies + timeout;
> - trace_rcu_grace_period(rsp->name,
> - READ_ONCE(rsp->gpnum),
> - TPS("fqsend"));
> - } else {
> - /* Deal with stray signal. */
> - WARN_ON(signal_pending(current));
> - trace_rcu_grace_period(rsp->name,
> - READ_ONCE(rsp->gpnum),
> - TPS("fqswaitsig"));
> - }
> - cond_resched_rcu_qs();
> - WRITE_ONCE(rsp->gp_activity, jiffies);
> - /*
> - * Count the remaining timeout when it was a spurious
> - * wakeup. Well, it is useful also when we have slept
> - * in the cond_resched().
> - */
> - j = jiffies;
> - if (ULONG_CMP_GE(j, rsp->jiffies_force_qs))
> - goto try_again;
> - timeout = rsp->jiffies_force_qs - j;
> - }
> + trace_rcu_grace_period(rsp->name,
> + READ_ONCE(rsp->gpnum),
> + TPS("fqswait"));
> + rsp->gp_state = RCU_GP_WAIT_FQS;
> + queue_delayed_kthread_work(rsp->gp_worker,
> + &rsp->gp_handle_qs_work,
> + timeout);
> + return;
> + }
> +
> + cond_resched_rcu_qs();
> + WRITE_ONCE(rsp->gp_activity, jiffies);
> + WARN_ON(signal_pending(current));
> + trace_rcu_grace_period(rsp->name,
> + READ_ONCE(rsp->gpnum),
> + TPS("reqwaitsig"));
> + trace_rcu_grace_period(rsp->name,
> + READ_ONCE(rsp->gpnum),
> + TPS("reqwait"));
> +}
> +
> +/*
> + * Function for RCU kthread work that handles a quiescent state
> + * and closes the related grace period.
> + */
> +static void rcu_gp_handle_qs_func(struct kthread_work *work)
> +{
> + unsigned long timeout, j;
> + struct rcu_state *rsp = container_of(work, struct rcu_state,
> + gp_handle_qs_work.work);
> + struct rcu_node *rnp = rcu_get_root(rsp);
> +
>
> + /*
> + * There is a small race window in rcu_gp_kthread_worker_poke()
> + * when the work might be queued more times. First, check if
> + * we are already waiting for the GP start instead.
> + */
> + if (!rcu_gp_in_progress(rsp)) {
> + if (rcu_gp_start_ready(rsp))
> + queue_kthread_work(rsp->gp_worker, &rsp->gp_start_work);
> + return;
> + }
> +
> + /*
> + * Second, we might have been queued more times to force QS.
> + * Just continue waiting if we have already forced it.
> + */
> + if (!rcu_gp_handle_qs_ready(rsp) &&
> + ULONG_CMP_LT(jiffies, rsp->jiffies_force_qs))
> + goto wait_continue;
> +
> + rsp->gp_state = RCU_GP_DOING_FQS;
> +try_again:
> + /* Locking provides needed memory barriers. */
> + /* If grace period done, leave loop. */
> + if (!READ_ONCE(rnp->qsmask) &&
> + !rcu_preempt_blocked_readers_cgp(rnp)) {
> /* Handle grace-period end. */
> rsp->gp_state = RCU_GP_CLEANUP;
> rcu_gp_cleanup(rsp);
> rsp->gp_state = RCU_GP_CLEANED;
> + trace_rcu_grace_period(rsp->name,
> + READ_ONCE(rsp->gpnum),
> + TPS("reqwait"));
> + rsp->gp_state = RCU_GP_WAIT_GPS;
> + return;
> + }
> +
> + /* If time for quiescent-state forcing, do it. */
> + if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
> + (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS)) {
> + trace_rcu_grace_period(rsp->name,
> + READ_ONCE(rsp->gpnum),
> + TPS("fqsstart"));
> + rcu_gp_fqs(rsp);
> + timeout = normalize_jiffies_till_next_fqs();
> + rsp->jiffies_force_qs = jiffies + timeout;
> + trace_rcu_grace_period(rsp->name,
> + READ_ONCE(rsp->gpnum),
> + TPS("fqsend"));
> + } else {
> + /* Deal with stray signal. */
> + WARN_ON(signal_pending(current));
> + trace_rcu_grace_period(rsp->name,
> + READ_ONCE(rsp->gpnum),
> + TPS("fqswaitsig"));
> }
> +wait_continue:
> + cond_resched_rcu_qs();
> + WRITE_ONCE(rsp->gp_activity, jiffies);
> + /*
> + * Count the remaining timeout when it was a spurious
> + * wakeup. Well, it is useful also when we have slept
> + * in the cond_resched().
> + */
> + j = jiffies;
> + if (ULONG_CMP_GE(j, rsp->jiffies_force_qs))
> + goto try_again;
> + timeout = rsp->jiffies_force_qs - j;
> +
> + trace_rcu_grace_period(rsp->name,
> + READ_ONCE(rsp->gpnum),
> + TPS("fqswait"));
> + rsp->gp_state = RCU_GP_WAIT_FQS;
> + queue_delayed_kthread_work(rsp->gp_worker, &rsp->gp_handle_qs_work,
> + timeout);
> }
>
> /*
> @@ -2172,7 +2263,7 @@ static bool
> rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
> struct rcu_data *rdp)
> {
> - if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
> + if (!rsp->gp_worker || !cpu_needs_another_gp(rsp, rdp)) {
> /*
> * Either we have not yet spawned the grace-period
> * task, this CPU does not need another grace period,
> @@ -2234,7 +2325,7 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
> WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
> WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
> raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
> - rcu_gp_kthread_wake(rsp);
> + rcu_gp_kthread_worker_poke(rsp);
> }
>
> /*
> @@ -2355,7 +2446,7 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
> {
> unsigned long flags;
> unsigned long mask;
> - bool needwake;
> + bool needpoke;
> struct rcu_node *rnp;
>
> rnp = rdp->mynode;
> @@ -2387,12 +2478,12 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
> * This GP can't end until cpu checks in, so all of our
> * callbacks can be processed during the next GP.
> */
> - needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
> + needpoke = rcu_accelerate_cbs(rsp, rnp, rdp);
>
> rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
> /* ^^^ Released rnp->lock */
> - if (needwake)
> - rcu_gp_kthread_wake(rsp);
> + if (needpoke)
> + rcu_gp_kthread_worker_poke(rsp);
> }
> }
>
> @@ -2895,7 +2986,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
> }
> WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
> raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
> - rcu_gp_kthread_wake(rsp);
> + rcu_gp_kthread_worker_poke(rsp);
> }
>
> /*
> @@ -2907,7 +2998,7 @@ static void
> __rcu_process_callbacks(struct rcu_state *rsp)
> {
> unsigned long flags;
> - bool needwake;
> + bool needpoke;
> struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
>
> WARN_ON_ONCE(rdp->beenonline == 0);
> @@ -2919,10 +3010,10 @@ __rcu_process_callbacks(struct rcu_state *rsp)
> local_irq_save(flags);
> if (cpu_needs_another_gp(rsp, rdp)) {
> raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
> - needwake = rcu_start_gp(rsp);
> + needpoke = rcu_start_gp(rsp);
> raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
> - if (needwake)
> - rcu_gp_kthread_wake(rsp);
> + if (needpoke)
> + rcu_gp_kthread_worker_poke(rsp);
> } else {
> local_irq_restore(flags);
> }
> @@ -2980,7 +3071,7 @@ static void invoke_rcu_core(void)
> static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
> struct rcu_head *head, unsigned long flags)
> {
> - bool needwake;
> + bool needpoke;
>
> /*
> * If called from an extended quiescent state, invoke the RCU
> @@ -3011,10 +3102,10 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
>
> raw_spin_lock(&rnp_root->lock);
> smp_mb__after_unlock_lock();
> - needwake = rcu_start_gp(rsp);
> + needpoke = rcu_start_gp(rsp);
> raw_spin_unlock(&rnp_root->lock);
> - if (needwake)
> - rcu_gp_kthread_wake(rsp);
> + if (needpoke)
> + rcu_gp_kthread_worker_poke(rsp);
> } else {
> /* Give the grace period a kick. */
> rdp->blimit = LONG_MAX;
> @@ -4044,7 +4135,7 @@ static int __init rcu_spawn_gp_kthread(void)
> struct rcu_node *rnp;
> struct rcu_state *rsp;
> struct sched_param sp;
> - struct task_struct *t;
> + struct kthread_worker *w;
>
> /* Force priority into range. */
> if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
> @@ -4059,16 +4150,20 @@ static int __init rcu_spawn_gp_kthread(void)
>
> rcu_scheduler_fully_active = 1;
> for_each_rcu_flavor(rsp) {
> - t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
> - BUG_ON(IS_ERR(t));
> + init_kthread_work(&rsp->gp_init_work, rcu_gp_init_func);
> + init_kthread_work(&rsp->gp_start_work, rcu_gp_start_func);
> + init_delayed_kthread_work(&rsp->gp_handle_qs_work,
> + rcu_gp_handle_qs_func);
> + w = create_kthread_worker("%s", rsp->name);
> + BUG_ON(IS_ERR(w));
> rnp = rcu_get_root(rsp);
> raw_spin_lock_irqsave(&rnp->lock, flags);
> - rsp->gp_kthread = t;
> + rsp->gp_worker = w;
> if (kthread_prio) {
> sp.sched_priority = kthread_prio;
> - sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
> + sched_setscheduler_nocheck(w->task, SCHED_FIFO, &sp);
> }
> - wake_up_process(t);
> + queue_kthread_work(w, &rsp->gp_init_work);
> raw_spin_unlock_irqrestore(&rnp->lock, flags);
> }
> rcu_spawn_nocb_kthreads();
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index f16578a5eefe..b9490e975dd7 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -25,6 +25,7 @@
> #include <linux/cache.h>
> #include <linux/spinlock.h>
> #include <linux/threads.h>
> +#include <linux/kthread.h>
> #include <linux/cpumask.h>
> #include <linux/seqlock.h>
> #include <linux/stop_machine.h>
> @@ -466,7 +467,12 @@ struct rcu_state {
> /* Subject to priority boost. */
> unsigned long gpnum; /* Current gp number. */
> unsigned long completed; /* # of last completed gp. */
> - struct task_struct *gp_kthread; /* Task for grace periods. */
> + struct kthread_worker *gp_worker; /* Worker for grace periods */
> + struct kthread_work gp_init_work; /* Init work for handling gp */
> + struct kthread_work gp_start_work; /* Work for starting gp */
> + struct delayed_kthread_work
> + gp_handle_qs_work; /* Work for QS state handling */
> +
> wait_queue_head_t gp_wq; /* Where GP task waits. */
> short gp_flags; /* Commands for GP task. */
> short gp_state; /* GP kthread sleep state. */
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index b2bf3963a0ae..55ae68530b7a 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1476,7 +1476,7 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt)
> */
> static void rcu_prepare_for_idle(void)
> {
> - bool needwake;
> + bool needpoke;
> struct rcu_data *rdp;
> struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
> struct rcu_node *rnp;
> @@ -1528,10 +1528,10 @@ static void rcu_prepare_for_idle(void)
> rnp = rdp->mynode;
> raw_spin_lock(&rnp->lock); /* irqs already disabled. */
> smp_mb__after_unlock_lock();
> - needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
> + needpoke = rcu_accelerate_cbs(rsp, rnp, rdp);
> raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
> - if (needwake)
> - rcu_gp_kthread_wake(rsp);
> + if (needpoke)
> + rcu_gp_kthread_worker_poke(rsp);
> }
> }
>
> @@ -2020,15 +2020,15 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
> unsigned long c;
> bool d;
> unsigned long flags;
> - bool needwake;
> + bool needpoke;
> struct rcu_node *rnp = rdp->mynode;
>
> raw_spin_lock_irqsave(&rnp->lock, flags);
> smp_mb__after_unlock_lock();
> - needwake = rcu_start_future_gp(rnp, rdp, &c);
> + needpoke = rcu_start_future_gp(rnp, rdp, &c);
> raw_spin_unlock_irqrestore(&rnp->lock, flags);
> - if (needwake)
> - rcu_gp_kthread_wake(rdp->rsp);
> + if (needpoke)
> + rcu_gp_kthread_worker_poke(rdp->rsp);
>
> /*
> * Wait for the grace period. Do so interruptibly to avoid messing
> --
> 1.8.5.6
>
--
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