[patch RT 3/3] workqueue: Revert workqueue: Fix cpuhotplug trainwreck

From: Thomas Gleixner
Date: Mon Jul 16 2012 - 04:08:14 EST

Revert

Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Date: Fri Sep 30 11:57:58 2011 +0200
workqueue: Fix cpuhotplug trainwreck

As TREAD_BOUND no longer affects cpu down, and this code introduced
a lot of races with taking down a CPU.

Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
include/linux/cpu.h | 6 +-
include/linux/workqueue.h | 5 +-
kernel/workqueue.c | 561 +++++++++++++++++++++++++++++++++------------
3 files changed, 415 insertions(+), 157 deletions(-)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index a6bda1b..00d2f6f8 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -75,10 +75,8 @@ enum {
/* migration should happen before other stuff but after perf */
CPU_PRI_PERF = 20,
CPU_PRI_MIGRATION = 10,
-
- CPU_PRI_WORKQUEUE_ACTIVE = 5, /* prepare workqueues for others */
- CPU_PRI_NORMAL = 0,
- CPU_PRI_WORKQUEUE_INACTIVE = -5, /* flush workqueues after others */
+ /* prepare workqueues for other notifiers */
+ CPU_PRI_WORKQUEUE = 5,
};

#define CPU_ONLINE 0x0002 /* CPU (unsigned)v is up */
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 9849be1..af15545 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -254,10 +254,9 @@ enum {
WQ_MEM_RECLAIM = 1 << 3, /* may be used for memory reclaim */
WQ_HIGHPRI = 1 << 4, /* high priority */
WQ_CPU_INTENSIVE = 1 << 5, /* cpu instensive workqueue */
- WQ_NON_AFFINE = 1 << 6, /* free to move works around cpus */

- WQ_DRAINING = 1 << 7, /* internal: workqueue is draining */
- WQ_RESCUER = 1 << 8, /* internal: workqueue has rescuer */
+ WQ_DRAINING = 1 << 6, /* internal: workqueue is draining */
+ WQ_RESCUER = 1 << 7, /* internal: workqueue has rescuer */

WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1e7f9c7..33d1095 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -41,7 +41,6 @@
#include <linux/debug_locks.h>
#include <linux/lockdep.h>
#include <linux/idr.h>
-#include <linux/delay.h>

#include "workqueue_sched.h"

@@ -58,10 +57,20 @@ enum {
WORKER_DIE = 1 << 1, /* die die die */
WORKER_IDLE = 1 << 2, /* is idle */
WORKER_PREP = 1 << 3, /* preparing to run works */
- WORKER_CPU_INTENSIVE = 1 << 4, /* cpu intensive */
- WORKER_UNBOUND = 1 << 5, /* worker is unbound */
+ WORKER_ROGUE = 1 << 4, /* not bound to any cpu */
+ WORKER_REBIND = 1 << 5, /* mom is home, come back */
+ WORKER_CPU_INTENSIVE = 1 << 6, /* cpu intensive */
+ WORKER_UNBOUND = 1 << 7, /* worker is unbound */

- WORKER_NOT_RUNNING = WORKER_PREP | WORKER_CPU_INTENSIVE | WORKER_UNBOUND,
+ WORKER_NOT_RUNNING = WORKER_PREP | WORKER_ROGUE | WORKER_REBIND |
+ WORKER_CPU_INTENSIVE | WORKER_UNBOUND,
+
+ /* gcwq->trustee_state */
+ TRUSTEE_START = 0, /* start */
+ TRUSTEE_IN_CHARGE = 1, /* trustee in charge of gcwq */
+ TRUSTEE_BUTCHER = 2, /* butcher workers */
+ TRUSTEE_RELEASE = 3, /* release workers */
+ TRUSTEE_DONE = 4, /* trustee is done */

BUSY_WORKER_HASH_ORDER = 6, /* 64 pointers */
BUSY_WORKER_HASH_SIZE = 1 << BUSY_WORKER_HASH_ORDER,
@@ -75,6 +84,7 @@ enum {
(min two ticks) */
MAYDAY_INTERVAL = HZ / 10, /* and then every 100ms */
CREATE_COOLDOWN = HZ, /* time to breath after fail */
+ TRUSTEE_COOLDOWN = HZ / 10, /* for trustee draining */

/*
* Rescue workers are used only on emergencies and shared by
@@ -126,6 +136,7 @@ struct worker {
unsigned long last_active; /* L: last active timestamp */
unsigned int flags; /* X: flags */
int id; /* I: worker id */
+ struct work_struct rebind_work; /* L: rebind worker to cpu */
int sleeping; /* None */
};

@@ -153,8 +164,10 @@ struct global_cwq {

struct ida worker_ida; /* L: for worker IDs */

+ struct task_struct *trustee; /* L: for gcwq shutdown */
+ unsigned int trustee_state; /* L: trustee state */
+ wait_queue_head_t trustee_wait; /* trustee wait */
struct worker *first_idle; /* L: first idle worker */
- wait_queue_head_t idle_wait;
} ____cacheline_aligned_in_smp;

/*
@@ -956,38 +969,13 @@ static bool is_chained_work(struct workqueue_struct *wq)
return false;
}

-static void ___queue_work(struct workqueue_struct *wq, struct global_cwq *gcwq,
- struct work_struct *work)
-{
- struct cpu_workqueue_struct *cwq;
- struct list_head *worklist;
- unsigned int work_flags;
-
- /* gcwq determined, get cwq and queue */
- cwq = get_cwq(gcwq->cpu, wq);
- trace_workqueue_queue_work(gcwq->cpu, cwq, work);
-
- BUG_ON(!list_empty(&work->entry));
-
- cwq->nr_in_flight[cwq->work_color]++;
- work_flags = work_color_to_flags(cwq->work_color);
-
- if (likely(cwq->nr_active < cwq->max_active)) {
- trace_workqueue_activate_work(work);
- cwq->nr_active++;
- worklist = gcwq_determine_ins_pos(gcwq, cwq);
- } else {
- work_flags |= WORK_STRUCT_DELAYED;
- worklist = &cwq->delayed_works;
- }
-
- insert_work(cwq, work, worklist, work_flags);
-}
-
static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
struct work_struct *work)
{
struct global_cwq *gcwq;
+ struct cpu_workqueue_struct *cwq;
+ struct list_head *worklist;
+ unsigned int work_flags;
unsigned long flags;

debug_work_activate(work);
@@ -1033,32 +1021,27 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
spin_lock_irqsave(&gcwq->lock, flags);
}

- ___queue_work(wq, gcwq, work);
+ /* gcwq determined, get cwq and queue */
+ cwq = get_cwq(gcwq->cpu, wq);
+ trace_workqueue_queue_work(cpu, cwq, work);

- spin_unlock_irqrestore(&gcwq->lock, flags);
-}
+ BUG_ON(!list_empty(&work->entry));

-/**
- * queue_work_on - queue work on specific cpu
- * @cpu: CPU number to execute work on
- * @wq: workqueue to use
- * @work: work to queue
- *
- * Returns 0 if @work was already on a queue, non-zero otherwise.
- *
- * We queue the work to a specific CPU, the caller must ensure it
- * can't go away.
- */
-static int
-__queue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work)
-{
- int ret = 0;
+ cwq->nr_in_flight[cwq->work_color]++;
+ work_flags = work_color_to_flags(cwq->work_color);

- if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
- __queue_work(cpu, wq, work);
- ret = 1;
+ if (likely(cwq->nr_active < cwq->max_active)) {
+ trace_workqueue_activate_work(work);
+ cwq->nr_active++;
+ worklist = gcwq_determine_ins_pos(gcwq, cwq);
+ } else {
+ work_flags |= WORK_STRUCT_DELAYED;
+ worklist = &cwq->delayed_works;
}
- return ret;
+
+ insert_work(cwq, work, worklist, work_flags);
+
+ spin_unlock_irqrestore(&gcwq->lock, flags);
}

/**
@@ -1075,19 +1058,34 @@ int queue_work(struct workqueue_struct *wq, struct work_struct *work)
{
int ret;

- ret = __queue_work_on(get_cpu_light(), wq, work);
+ ret = queue_work_on(get_cpu_light(), wq, work);
put_cpu_light();

return ret;
}
EXPORT_SYMBOL_GPL(queue_work);

+/**
+ * queue_work_on - queue work on specific cpu
+ * @cpu: CPU number to execute work on
+ * @wq: workqueue to use
+ * @work: work to queue
+ *
+ * Returns 0 if @work was already on a queue, non-zero otherwise.
+ *
+ * We queue the work to a specific CPU, the caller must ensure it
+ * can't go away.
+ */
int
queue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work)
{
- WARN_ON(wq->flags & WQ_NON_AFFINE);
+ int ret = 0;

- return __queue_work_on(cpu, wq, work);
+ if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
+ __queue_work(cpu, wq, work);
+ ret = 1;
+ }
+ return ret;
}
EXPORT_SYMBOL_GPL(queue_work_on);

@@ -1133,8 +1131,6 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
struct timer_list *timer = &dwork->timer;
struct work_struct *work = &dwork->work;

- WARN_ON((wq->flags & WQ_NON_AFFINE) && cpu != -1);
-
if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
unsigned int lcpu;

@@ -1200,13 +1196,12 @@ static void worker_enter_idle(struct worker *worker)
/* idle_list is LIFO */
list_add(&worker->entry, &gcwq->idle_list);

- if (gcwq->nr_idle == gcwq->nr_workers)
- wake_up_all(&gcwq->idle_wait);
-
- if (too_many_workers(gcwq) && !timer_pending(&gcwq->idle_timer)) {
- mod_timer(&gcwq->idle_timer,
- jiffies + IDLE_WORKER_TIMEOUT);
- }
+ if (likely(!(worker->flags & WORKER_ROGUE))) {
+ if (too_many_workers(gcwq) && !timer_pending(&gcwq->idle_timer))
+ mod_timer(&gcwq->idle_timer,
+ jiffies + IDLE_WORKER_TIMEOUT);
+ } else
+ wake_up_all(&gcwq->trustee_wait);

/* sanity check nr_running */
WARN_ON_ONCE(gcwq->nr_workers == gcwq->nr_idle &&
@@ -1298,6 +1293,23 @@ __acquires(&gcwq->lock)
}
}

+/*
+ * Function for worker->rebind_work used to rebind rogue busy workers
+ * to the associated cpu which is coming back online. This is
+ * scheduled by cpu up but can race with other cpu hotplug operations
+ * and may be executed twice without intervening cpu down.
+ */
+static void worker_rebind_fn(struct work_struct *work)
+{
+ struct worker *worker = container_of(work, struct worker, rebind_work);
+ struct global_cwq *gcwq = worker->gcwq;
+
+ if (worker_maybe_bind_and_lock(worker))
+ worker_clr_flags(worker, WORKER_REBIND);
+
+ spin_unlock_irq(&gcwq->lock);
+}
+
static struct worker *alloc_worker(void)
{
struct worker *worker;
@@ -1306,6 +1318,7 @@ static struct worker *alloc_worker(void)
if (worker) {
INIT_LIST_HEAD(&worker->entry);
INIT_LIST_HEAD(&worker->scheduled);
+ INIT_WORK(&worker->rebind_work, worker_rebind_fn);
/* on creation a worker is in !idle && prep state */
worker->flags = WORKER_PREP;
}
@@ -1645,6 +1658,13 @@ static bool manage_workers(struct worker *worker)

gcwq->flags &= ~GCWQ_MANAGING_WORKERS;

+ /*
+ * The trustee might be waiting to take over the manager
+ * position, tell it we're done.
+ */
+ if (unlikely(gcwq->trustee))
+ wake_up_all(&gcwq->trustee_wait);
+
return ret;
}

@@ -3185,76 +3205,171 @@ EXPORT_SYMBOL_GPL(work_busy);
* gcwqs serve mix of short, long and very long running works making
* blocked draining impractical.
*
+ * This is solved by allowing a gcwq to be detached from CPU, running
+ * it with unbound (rogue) workers and allowing it to be reattached
+ * later if the cpu comes back online. A separate thread is created
+ * to govern a gcwq in such state and is called the trustee of the
+ * gcwq.
+ *
+ * Trustee states and their descriptions.
+ *
+ * START Command state used on startup. On CPU_DOWN_PREPARE, a
+ * new trustee is started with this state.
+ *
+ * IN_CHARGE Once started, trustee will enter this state after
+ * assuming the manager role and making all existing
+ * workers rogue. DOWN_PREPARE waits for trustee to
+ * enter this state. After reaching IN_CHARGE, trustee
+ * tries to execute the pending worklist until it's empty
+ * and the state is set to BUTCHER, or the state is set
+ * to RELEASE.
+ *
+ * BUTCHER Command state which is set by the cpu callback after
+ * the cpu has went down. Once this state is set trustee
+ * knows that there will be no new works on the worklist
+ * and once the worklist is empty it can proceed to
+ * killing idle workers.
+ *
+ * RELEASE Command state which is set by the cpu callback if the
+ * cpu down has been canceled or it has come online
+ * again. After recognizing this state, trustee stops
+ * trying to drain or butcher and clears ROGUE, rebinds
+ * all remaining workers back to the cpu and releases
+ * manager role.
+ *
+ * DONE Trustee will enter this state after BUTCHER or RELEASE
+ * is complete.
+ *
+ * trustee CPU draining
+ * took over down complete
+ * START -----------> IN_CHARGE -----------> BUTCHER -----------> DONE
+ * | | ^
+ * | CPU is back online v return workers |
+ * ----------------> RELEASE --------------
*/

-static int __devinit workqueue_cpu_up_callback(struct notifier_block *nfb,
- unsigned long action,
- void *hcpu)
-{
- unsigned int cpu = (unsigned long)hcpu;
- struct global_cwq *gcwq = get_gcwq(cpu);
- struct worker *uninitialized_var(new_worker);
- unsigned long flags;
+/**
+ * trustee_wait_event_timeout - timed event wait for trustee
+ * @cond: condition to wait for
+ * @timeout: timeout in jiffies
+ *
+ * wait_event_timeout() for trustee to use. Handles locking and
+ * checks for RELEASE request.
+ *
+ * CONTEXT:
+ * spin_lock_irq(gcwq->lock) which may be released and regrabbed
+ * multiple times. To be used by trustee.
+ *
+ * RETURNS:
+ * Positive indicating left time if @cond is satisfied, 0 if timed
+ * out, -1 if canceled.
+ */
+#define trustee_wait_event_timeout(cond, timeout) ({ \
+ long __ret = (timeout); \
+ while (!((cond) || (gcwq->trustee_state == TRUSTEE_RELEASE)) && \
+ __ret) { \
+ spin_unlock_irq(&gcwq->lock); \
+ __wait_event_timeout(gcwq->trustee_wait, (cond) || \
+ (gcwq->trustee_state == TRUSTEE_RELEASE), \
+ __ret); \
+ spin_lock_irq(&gcwq->lock); \
+ } \
+ gcwq->trustee_state == TRUSTEE_RELEASE ? -1 : (__ret); \
+})

- action &= ~CPU_TASKS_FROZEN;
+/**
+ * trustee_wait_event - event wait for trustee
+ * @cond: condition to wait for
+ *
+ * wait_event() for trustee to use. Automatically handles locking and
+ * checks for CANCEL request.
+ *
+ * CONTEXT:
+ * spin_lock_irq(gcwq->lock) which may be released and regrabbed
+ * multiple times. To be used by trustee.
+ *
+ * RETURNS:
+ * 0 if @cond is satisfied, -1 if canceled.
+ */
+#define trustee_wait_event(cond) ({ \
+ long __ret1; \
+ __ret1 = trustee_wait_event_timeout(cond, MAX_SCHEDULE_TIMEOUT);\
+ __ret1 < 0 ? -1 : 0; \
+})

- switch (action) {
- case CPU_UP_PREPARE:
- BUG_ON(gcwq->first_idle);
- new_worker = create_worker(gcwq, false);
- if (!new_worker)
- return NOTIFY_BAD;
- case CPU_UP_CANCELED:
- case CPU_ONLINE:
- break;
- default:
- return notifier_from_errno(0);
- }
+static int __cpuinit trustee_thread(void *__gcwq)
+{
+ struct global_cwq *gcwq = __gcwq;
+ struct worker *worker;
+ struct work_struct *work;
+ struct hlist_node *pos;
+ long rc;
+ int i;

- /* some are called w/ irq disabled, don't disturb irq status */
- spin_lock_irqsave(&gcwq->lock, flags);
+ BUG_ON(gcwq->cpu != smp_processor_id());

- switch (action) {
- case CPU_UP_PREPARE:
- BUG_ON(gcwq->first_idle);
- gcwq->first_idle = new_worker;
- break;
+ spin_lock_irq(&gcwq->lock);
+ /*
+ * Claim the manager position and make all workers rogue.
+ * Trustee must be bound to the target cpu and can't be
+ * cancelled.
+ */
+ BUG_ON(gcwq->cpu != smp_processor_id());
+ rc = trustee_wait_event(!(gcwq->flags & GCWQ_MANAGING_WORKERS));
+ BUG_ON(rc < 0);

- case CPU_UP_CANCELED:
- destroy_worker(gcwq->first_idle);
- gcwq->first_idle = NULL;
- break;
+ gcwq->flags |= GCWQ_MANAGING_WORKERS;

- case CPU_ONLINE:
- spin_unlock_irq(&gcwq->lock);
- kthread_bind(gcwq->first_idle->task, cpu);
- spin_lock_irq(&gcwq->lock);
- gcwq->flags |= GCWQ_MANAGE_WORKERS;
- start_worker(gcwq->first_idle);
- gcwq->first_idle = NULL;
- break;
- }
+ list_for_each_entry(worker, &gcwq->idle_list, entry)
+ worker->flags |= WORKER_ROGUE;

- spin_unlock_irqrestore(&gcwq->lock, flags);
+ for_each_busy_worker(worker, i, pos, gcwq)
+ worker->flags |= WORKER_ROGUE;

- return notifier_from_errno(0);
-}
+ /*
+ * Call schedule() so that we cross rq->lock and thus can
+ * guarantee sched callbacks see the rogue flag. This is
+ * necessary as scheduler callbacks may be invoked from other
+ * cpus.
+ */
+ spin_unlock_irq(&gcwq->lock);
+ schedule();
+ spin_lock_irq(&gcwq->lock);

-static void flush_gcwq(struct global_cwq *gcwq)
-{
- struct work_struct *work, *nw;
- struct worker *worker, *n;
- LIST_HEAD(non_affine_works);
+ /*
+ * Sched callbacks are disabled now. Zap nr_running. After
+ * this, nr_running stays zero and need_more_worker() and
+ * keep_working() are always true as long as the worklist is
+ * not empty.
+ */
+ atomic_set(get_gcwq_nr_running(gcwq->cpu), 0);

+ spin_unlock_irq(&gcwq->lock);
+ del_timer_sync(&gcwq->idle_timer);
spin_lock_irq(&gcwq->lock);
- list_for_each_entry_safe(work, nw, &gcwq->worklist, entry) {
- struct workqueue_struct *wq = get_work_cwq(work)->wq;

- if (wq->flags & WQ_NON_AFFINE)
- list_move(&work->entry, &non_affine_works);
- }
+ /*
+ * We're now in charge. Notify and proceed to drain. We need
+ * to keep the gcwq running during the whole CPU down
+ * procedure as other cpu hotunplug callbacks may need to
+ * flush currently running tasks.
+ */
+ gcwq->trustee_state = TRUSTEE_IN_CHARGE;
+ wake_up_all(&gcwq->trustee_wait);

- while (!list_empty(&gcwq->worklist)) {
+ /*
+ * The original cpu is in the process of dying and may go away
+ * anytime now. When that happens, we and all workers would
+ * be migrated to other cpus. Try draining any left work. We
+ * want to get it over with ASAP - spam rescuers, wake up as
+ * many idlers as necessary and create new ones till the
+ * worklist is empty. Note that if the gcwq is frozen, there
+ * may be frozen works in freezable cwqs. Don't declare
+ * completion while frozen.
+ */
+ while (gcwq->nr_workers != gcwq->nr_idle ||
+ gcwq->flags & GCWQ_FREEZING ||
+ gcwq->trustee_state == TRUSTEE_IN_CHARGE) {
int nr_works = 0;

list_for_each_entry(work, &gcwq->worklist, entry) {
@@ -3268,55 +3383,200 @@ static void flush_gcwq(struct global_cwq *gcwq)
wake_up_process(worker->task);
}

- spin_unlock_irq(&gcwq->lock);
-
if (need_to_create_worker(gcwq)) {
- worker = create_worker(gcwq, true);
- if (worker)
+ spin_unlock_irq(&gcwq->lock);
+ worker = create_worker(gcwq, false);
+ spin_lock_irq(&gcwq->lock);
+ if (worker) {
+ worker->flags |= WORKER_ROGUE;
start_worker(worker);
+ }
}

- wait_event_timeout(gcwq->idle_wait,
- gcwq->nr_idle == gcwq->nr_workers, HZ/10);
-
- spin_lock_irq(&gcwq->lock);
+ /* give a breather */
+ if (trustee_wait_event_timeout(false, TRUSTEE_COOLDOWN) < 0)
+ break;
}

- WARN_ON(gcwq->nr_workers != gcwq->nr_idle);
+ /*
+ * Either all works have been scheduled and cpu is down, or
+ * cpu down has already been canceled. Wait for and butcher
+ * all workers till we're canceled.
+ */
+ do {
+ rc = trustee_wait_event(!list_empty(&gcwq->idle_list));
+ while (!list_empty(&gcwq->idle_list))
+ destroy_worker(list_first_entry(&gcwq->idle_list,
+ struct worker, entry));
+ } while (gcwq->nr_workers && rc >= 0);

- list_for_each_entry_safe(worker, n, &gcwq->idle_list, entry)
- destroy_worker(worker);
+ /*
+ * At this point, either draining has completed and no worker
+ * is left, or cpu down has been canceled or the cpu is being
+ * brought back up. There shouldn't be any idle one left.
+ * Tell the remaining busy ones to rebind once it finishes the
+ * currently scheduled works by scheduling the rebind_work.
+ */
+ WARN_ON(!list_empty(&gcwq->idle_list));

- WARN_ON(gcwq->nr_workers || gcwq->nr_idle);
+ for_each_busy_worker(worker, i, pos, gcwq) {
+ struct work_struct *rebind_work = &worker->rebind_work;

- spin_unlock_irq(&gcwq->lock);
+ /*
+ * Rebind_work may race with future cpu hotplug
+ * operations. Use a separate flag to mark that
+ * rebinding is scheduled.
+ */
+ worker->flags |= WORKER_REBIND;
+ worker->flags &= ~WORKER_ROGUE;

- gcwq = get_gcwq(get_cpu_light());
- spin_lock_irq(&gcwq->lock);
- list_for_each_entry_safe(work, nw, &non_affine_works, entry) {
- list_del_init(&work->entry);
- ___queue_work(get_work_cwq(work)->wq, gcwq, work);
+ /* queue rebind_work, wq doesn't matter, use the default one */
+ if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
+ work_data_bits(rebind_work)))
+ continue;
+
+ debug_work_activate(rebind_work);
+ insert_work(get_cwq(gcwq->cpu, system_wq), rebind_work,
+ worker->scheduled.next,
+ work_color_to_flags(WORK_NO_COLOR));
}
+
+ /* relinquish manager role */
+ gcwq->flags &= ~GCWQ_MANAGING_WORKERS;
+
+ /* notify completion */
+ gcwq->trustee = NULL;
+ gcwq->trustee_state = TRUSTEE_DONE;
+ wake_up_all(&gcwq->trustee_wait);
spin_unlock_irq(&gcwq->lock);
- put_cpu_light();
+ return 0;
}

-static int __devinit workqueue_cpu_down_callback(struct notifier_block *nfb,
+/**
+ * wait_trustee_state - wait for trustee to enter the specified state
+ * @gcwq: gcwq the trustee of interest belongs to
+ * @state: target state to wait for
+ *
+ * Wait for the trustee to reach @state. DONE is already matched.
+ *
+ * CONTEXT:
+ * spin_lock_irq(gcwq->lock) which may be released and regrabbed
+ * multiple times. To be used by cpu_callback.
+ */
+static void __cpuinit wait_trustee_state(struct global_cwq *gcwq, int state)
+__releases(&gcwq->lock)
+__acquires(&gcwq->lock)
+{
+ if (!(gcwq->trustee_state == state ||
+ gcwq->trustee_state == TRUSTEE_DONE)) {
+ spin_unlock_irq(&gcwq->lock);
+ __wait_event(gcwq->trustee_wait,
+ gcwq->trustee_state == state ||
+ gcwq->trustee_state == TRUSTEE_DONE);
+ spin_lock_irq(&gcwq->lock);
+ }
+}
+
+static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
unsigned long action,
void *hcpu)
{
unsigned int cpu = (unsigned long)hcpu;
struct global_cwq *gcwq = get_gcwq(cpu);
+ struct task_struct *new_trustee = NULL;
+ struct worker *uninitialized_var(new_worker);
+ unsigned long flags;

action &= ~CPU_TASKS_FROZEN;

- switch (action) {
- case CPU_DOWN_PREPARE:
- flush_gcwq(gcwq);
- break;
- }
+ switch (action) {
+ case CPU_DOWN_PREPARE:
+ new_trustee = kthread_create(trustee_thread, gcwq,
+ "workqueue_trustee/%d\n", cpu);
+ if (IS_ERR(new_trustee))
+ return notifier_from_errno(PTR_ERR(new_trustee));
+ kthread_bind(new_trustee, cpu);
+ /* fall through */
+ case CPU_UP_PREPARE:
+ BUG_ON(gcwq->first_idle);
+ new_worker = create_worker(gcwq, false);
+ if (!new_worker) {
+ if (new_trustee)
+ kthread_stop(new_trustee);
+ return NOTIFY_BAD;
+ }
+ break;
+ case CPU_POST_DEAD:
+ case CPU_UP_CANCELED:
+ case CPU_DOWN_FAILED:
+ case CPU_ONLINE:
+ break;
+ case CPU_DYING:
+ /*
+ * We access this lockless. We are on the dying CPU
+ * and called from stomp machine.
+ *
+ * Before this, the trustee and all workers except for
+ * the ones which are still executing works from
+ * before the last CPU down must be on the cpu. After
+ * this, they'll all be diasporas.
+ */
+ gcwq->flags |= GCWQ_DISASSOCIATED;
+ default:
+ goto out;
+ }
+
+ /* some are called w/ irq disabled, don't disturb irq status */
+ spin_lock_irqsave(&gcwq->lock, flags);
+
+ switch (action) {
+ case CPU_DOWN_PREPARE:
+ /* initialize trustee and tell it to acquire the gcwq */
+ BUG_ON(gcwq->trustee || gcwq->trustee_state != TRUSTEE_DONE);
+ gcwq->trustee = new_trustee;
+ gcwq->trustee_state = TRUSTEE_START;
+ wake_up_process(gcwq->trustee);
+ wait_trustee_state(gcwq, TRUSTEE_IN_CHARGE);
+ /* fall through */
+ case CPU_UP_PREPARE:
+ BUG_ON(gcwq->first_idle);
+ gcwq->first_idle = new_worker;
+ break;
+
+ case CPU_POST_DEAD:
+ gcwq->trustee_state = TRUSTEE_BUTCHER;
+ /* fall through */
+ case CPU_UP_CANCELED:
+ destroy_worker(gcwq->first_idle);
+ gcwq->first_idle = NULL;
+ break;

+ case CPU_DOWN_FAILED:
+ case CPU_ONLINE:
+ gcwq->flags &= ~GCWQ_DISASSOCIATED;
+ if (gcwq->trustee_state != TRUSTEE_DONE) {
+ gcwq->trustee_state = TRUSTEE_RELEASE;
+ wake_up_process(gcwq->trustee);
+ wait_trustee_state(gcwq, TRUSTEE_DONE);
+ }
+
+ /*
+ * Trustee is done and there might be no worker left.
+ * Put the first_idle in and request a real manager to
+ * take a look.
+ */
+ spin_unlock_irq(&gcwq->lock);
+ kthread_bind(gcwq->first_idle->task, cpu);
+ spin_lock_irq(&gcwq->lock);
+ gcwq->flags |= GCWQ_MANAGE_WORKERS;
+ start_worker(gcwq->first_idle);
+ gcwq->first_idle = NULL;
+ break;
+ }
+
+ spin_unlock_irqrestore(&gcwq->lock, flags);

+out:
return notifier_from_errno(0);
}

@@ -3513,8 +3773,7 @@ static int __init init_workqueues(void)
unsigned int cpu;
int i;

- cpu_notifier(workqueue_cpu_up_callback, CPU_PRI_WORKQUEUE_ACTIVE);
- hotcpu_notifier(workqueue_cpu_down_callback, CPU_PRI_WORKQUEUE_INACTIVE);
+ cpu_notifier(workqueue_cpu_callback, CPU_PRI_WORKQUEUE);

/* initialize gcwqs */
for_each_gcwq_cpu(cpu) {
@@ -3537,7 +3796,9 @@ static int __init init_workqueues(void)
(unsigned long)gcwq);

ida_init(&gcwq->worker_ida);
- init_waitqueue_head(&gcwq->idle_wait);
+
+ gcwq->trustee_state = TRUSTEE_DONE;
+ init_waitqueue_head(&gcwq->trustee_wait);
}

/* create the initial worker */
--
1.7.3.4



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