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Subject[PATCH 10/11 V5] workqueue: unbind/rebind without manager_mutex
Date
gcwq_unbind_fn() unbind manager by ->manager pointer.

rebinding-manger, unbinding/rebinding newly created worker are done by
other place. so we don't need manager_mutex any more.

Also change the comment of @bind accordingly.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
kernel/workqueue.c | 52 ++++++++++++++++------------------------------------
1 files changed, 16 insertions(+), 36 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 819c84e..5fb712a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1667,17 +1667,15 @@ static void busy_worker_rebind_fn(struct work_struct *work)
* add themselves back to idle_list if the gcwq is still associated.
*/
static void rebind_workers(struct global_cwq *gcwq)
- __releases(&gcwq->lock) __acquires(&gcwq->lock)
{
struct worker_pool *pool;
struct worker *worker, *n;
struct hlist_node *pos;
int i;

- lockdep_assert_held(&gcwq->lock);
+ spin_lock_irq(&gcwq->lock);

- for_each_worker_pool(pool, gcwq)
- lockdep_assert_held(&pool->manager_mutex);
+ gcwq->flags &= ~GCWQ_DISASSOCIATED;

/* exile and kick idle ones */
for_each_worker_pool(pool, gcwq) {
@@ -1714,6 +1712,8 @@ static void rebind_workers(struct global_cwq *gcwq)
worker->scheduled.next,
work_color_to_flags(WORK_NO_COLOR));
}
+
+ spin_unlock_irq(&gcwq->lock);
}

static struct worker *alloc_worker(void)
@@ -1981,11 +1981,14 @@ __acquires(&gcwq->lock)
bool bind;

/*
- * Note we have held the manage_mutex, so DISASSOCIATED can't be
- * flipped and it is correct that we calculate @bind only once
- * and then release the gcwq->lock.
+ * Snapshot the value of @bind.
+ * Because the %UNBOUND bit of manager can't be cleared while it
+ * is creating worker. So we can detect whether the real @bind
+ * is/was changed and fix the newly created worker's binding in
+ * manager_start_worker().
*/
bind = !(gcwq->flags & GCWQ_DISASSOCIATED);
+ BUG_ON(!bind && !(pool->manager->flags & WORKER_UNBOUND));

if (!need_to_create_worker(pool))
return false;
@@ -3441,26 +3444,6 @@ EXPORT_SYMBOL_GPL(work_busy);
* cpu comes back online.
*/

-/* claim manager positions of all pools */
-static void gcwq_claim_management_and_lock(struct global_cwq *gcwq)
-{
- struct worker_pool *pool;
-
- for_each_worker_pool(pool, gcwq)
- mutex_lock_nested(&pool->manager_mutex, pool - gcwq->pools);
- spin_lock_irq(&gcwq->lock);
-}
-
-/* release manager positions */
-static void gcwq_release_management_and_unlock(struct global_cwq *gcwq)
-{
- struct worker_pool *pool;
-
- spin_unlock_irq(&gcwq->lock);
- for_each_worker_pool(pool, gcwq)
- mutex_unlock(&pool->manager_mutex);
-}
-
static void gcwq_unbind_fn(struct work_struct *work)
{
struct global_cwq *gcwq = get_gcwq(smp_processor_id());
@@ -3471,13 +3454,13 @@ static void gcwq_unbind_fn(struct work_struct *work)

BUG_ON(gcwq->cpu != smp_processor_id());

- gcwq_claim_management_and_lock(gcwq);
+ spin_lock_irq(&gcwq->lock);

/*
- * We've claimed all manager positions. Make all workers unbound
- * and set DISASSOCIATED. Before this, 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 may become diasporas.
+ * Make all workers unbound and set DISASSOCIATED.
+ * Before this, 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 may become diasporas.
*/
for_each_worker_pool(pool, gcwq) {
list_for_each_entry(worker, &pool->idle_list, entry)
@@ -3491,7 +3474,7 @@ static void gcwq_unbind_fn(struct work_struct *work)

gcwq->flags |= GCWQ_DISASSOCIATED;

- gcwq_release_management_and_unlock(gcwq);
+ spin_unlock_irq(&gcwq->lock);

/*
* Call schedule() so that we cross rq->lock and thus can guarantee
@@ -3547,10 +3530,7 @@ static int __devinit workqueue_cpu_up_callback(struct notifier_block *nfb,

case CPU_DOWN_FAILED:
case CPU_ONLINE:
- gcwq_claim_management_and_lock(gcwq);
- gcwq->flags &= ~GCWQ_DISASSOCIATED;
rebind_workers(gcwq);
- gcwq_release_management_and_unlock(gcwq);
break;
}
return NOTIFY_OK;
--
1.7.4.4


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