assoc_mutex is clear, it protects GCWQ_DISASSOCIATED.
And the C.S. of assoc_mutex is narrowed, it protects
create_worker()+start_worker() which require
GCWQ_DISASSOCIATED stable. don't need to protects
the whole manage_workers().
A result of narrowed C.S. maybe_rebind_manager()
has to be moved to the bottom of manage_workers().
Other result of narrowed C.S. manager_workers() becomes
simpler.
Signed-off-by: Lai Jiangshan <la...@cn.fujitsu.com>
---
kernel/workqueue.c | 63 ++++++++++++++++++++++++----------------------------
1 files changed, 29 insertions(+), 34 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 207b6a1..d9765c4 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -58,7 +58,7 @@ enum {
* be executing on any CPU. The gcwq behaves as an unbound one.
*
* Note that DISASSOCIATED can be flipped only while holding
- * managership of all pools on the gcwq to avoid changing binding
+ * assoc_mutex of all pools on the gcwq to avoid changing binding
* state while create_worker() is in progress.
*/
GCWQ_DISASSOCIATED = 1 << 0, /* cpu can't serve workers */
@@ -166,7 +166,7 @@ struct worker_pool {
struct timer_list mayday_timer; /* L: SOS timer for workers */
struct worker *manager; /* L: manager worker */
- struct mutex manager_mutex; /* mutex manager should hold */
+ struct mutex assoc_mutex; /* protect GCWQ_DISASSOCIATED */
struct ida worker_ida; /* L: for worker IDs */
};
@@ -1673,7 +1673,7 @@ static void rebind_workers(struct global_cwq *gcwq)
lockdep_assert_held(&gcwq->lock);
for_each_worker_pool(pool, gcwq)
- lockdep_assert_held(&pool->manager_mutex);
+ lockdep_assert_held(&pool->assoc_mutex);
/* set REBIND and kick idle ones */
for_each_worker_pool(pool, gcwq) {
@@ -1975,15 +1975,18 @@ restart:
while (true) {
struct worker *worker;
+ mutex_lock(&pool->assoc_mutex);
worker = create_worker(pool);
if (worker) {
del_timer_sync(&pool->mayday_timer);
spin_lock_irq(&gcwq->lock);
start_worker(worker);
BUG_ON(need_to_create_worker(pool));
+ mutex_unlock(&pool->assoc_mutex);
return true;
}
+ mutex_unlock(&pool->assoc_mutex);
if (!need_to_create_worker(pool))
break;
@@ -2040,7 +2043,7 @@ static bool maybe_destroy_workers(struct worker_pool
*pool)
}
/* does the manager need to be rebind after we just release gcwq->lock */
-static void maybe_rebind_manager(struct worker *manager)
+static bool maybe_rebind_manager(struct worker *manager)
{
struct global_cwq *gcwq = manager->pool->gcwq;
bool assoc = !(gcwq->flags & GCWQ_DISASSOCIATED);
@@ -2050,7 +2053,11 @@ static void maybe_rebind_manager(struct worker *manager)
if (worker_maybe_bind_and_lock(manager))
worker_clr_flags(manager, WORKER_UNBOUND);
+
+ return true;
}
+
+ return false;
}
/**
@@ -2061,9 +2068,7 @@ static void maybe_rebind_manager(struct worker *manager)
* to. At any given time, there can be only zero or one manager per
* gcwq. The exclusion is handled automatically by this function.
*
- * The caller can safely start processing works on false return. On
- * true return, it's guaranteed that need_to_create_worker() is false
- * and may_start_working() is true.
+ * The caller can safely start processing works on false return.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock) which may be released and regrabbed
@@ -2076,29 +2081,12 @@ static void maybe_rebind_manager(struct worker *manager)
static bool manage_workers(struct worker *worker)
{
struct worker_pool *pool = worker->pool;
- struct global_cwq *gcwq = pool->gcwq;
bool ret = false;
if (pool->manager)
return ret;
pool->manager = worker;
- if (unlikely(!mutex_trylock(&pool->manager_mutex))) {
- /*
- * Ouch! rebind_workers() or gcwq_unbind_fn() beats we.
- * it can't return false here, otherwise it will lead to
- * worker depletion. So we release gcwq->lock and then
- * grab manager_mutex again.
- */
- spin_unlock_irq(&gcwq->lock);
- mutex_lock(&pool->manager_mutex);
- spin_lock_irq(&gcwq->lock);
-
- /* rebind_workers() can happen when we release gcwq->lock */
- maybe_rebind_manager(worker);
- ret = true;
- }
-
pool->flags &= ~POOL_MANAGE_WORKERS;
/*
@@ -2108,7 +2096,14 @@ static bool manage_workers(struct worker *worker)
ret |= maybe_destroy_workers(pool);
ret |= maybe_create_worker(pool);
- mutex_unlock(&pool->manager_mutex);
+ /*
+ * rebind_workers() can happen while it does manage, so it has to
+ * check and do rebind by itself.
+ * Before rebind, it's guaranteed that need_to_create_worker() is
+ * false and may_start_working() is true here.
+ */
+ ret |= maybe_rebind_manager(worker);
+
pool->manager = NULL;
return ret;
@@ -3436,23 +3431,23 @@ EXPORT_SYMBOL_GPL(work_busy);
*/
/* claim manager positions of all pools */
-static void gcwq_claim_management_and_lock(struct global_cwq *gcwq)
+static void gcwq_claim_assoc_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);
+ mutex_lock_nested(&pool->assoc_mutex, pool - gcwq->pools);
spin_lock_irq(&gcwq->lock);
}
/* release manager positions */
-static void gcwq_release_management_and_unlock(struct global_cwq *gcwq)
+static void gcwq_release_assoc_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);
+ mutex_unlock(&pool->assoc_mutex);
}
static void gcwq_unbind_fn(struct work_struct *work)
@@ -3465,7 +3460,7 @@ static void gcwq_unbind_fn(struct work_struct *work)
BUG_ON(gcwq->cpu != smp_processor_id());
- gcwq_claim_management_and_lock(gcwq);
+ gcwq_claim_assoc_and_lock(gcwq);
/*
* We've claimed all manager positions. Make all workers unbound
@@ -3485,7 +3480,7 @@ static void gcwq_unbind_fn(struct work_struct *work)
gcwq->flags |= GCWQ_DISASSOCIATED;
- gcwq_release_management_and_unlock(gcwq);
+ gcwq_release_assoc_and_unlock(gcwq);
/*
* Call schedule() so that we cross rq->lock and thus can guarantee
@@ -3541,10 +3536,10 @@ 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_claim_assoc_and_lock(gcwq);
gcwq->flags &= ~GCWQ_DISASSOCIATED;
rebind_workers(gcwq);
- gcwq_release_management_and_unlock(gcwq);
+ gcwq_release_assoc_and_unlock(gcwq);
break;
}
return NOTIFY_OK;
@@ -3799,7 +3794,7 @@ static int __init init_workqueues(void)
(unsigned long)pool);
pool->manager = NULL;
- mutex_init(&pool->manager_mutex);
+ mutex_init(&pool->assoc_mutex);
ida_init(&pool->worker_ida);
}
}
--
1.7.4.4
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