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workqueue: use mutex for global_cwq manager exclusion

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POOL_MANAGING_WORKERS is used to ensure that at most one worker takes
the manager role at any given time on a given global_cwq.  Trustee
later hitched on it to assume manager adding blocking wait for the
bit.  As trustee already needed a custom wait mechanism, waiting for
MANAGING_WORKERS was rolled into the same mechanism.

Trustee is scheduled to be removed.  This patch separates out
MANAGING_WORKERS wait into per-pool mutex.  Workers use
mutex_trylock() to test for manager role and trustee uses mutex_lock()
to claim manager roles.

gcwq_claim/release_management() helpers are added to grab and release
manager roles of all pools on a global_cwq.  gcwq_claim_management()
always grabs pool manager mutexes in ascending pool index order and
uses pool index as lockdep subclass.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
This commit is contained in:
Tejun Heo 2012-07-17 12:39:27 -07:00
parent 403c821d45
commit 6037315269
1 changed files with 26 additions and 39 deletions
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65
kernel/workqueue.c
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@ -51,7 +51,6 @@ enum {
/* pool flags */
POOL_MANAGE_WORKERS = 1 << 0, /* need to manage workers */
POOL_MANAGING_WORKERS = 1 << 1, /* managing workers */
/* worker flags */
WORKER_STARTED = 1 << 0, /* started */
@ -155,6 +154,7 @@ struct worker_pool {
struct timer_list idle_timer; /* L: worker idle timeout */
struct timer_list mayday_timer; /* L: SOS timer for workers */
struct mutex manager_mutex; /* mutex manager should hold */
struct ida worker_ida; /* L: for worker IDs */
struct worker *first_idle; /* L: first idle worker */
};
@ -644,7 +644,7 @@ static bool need_to_manage_workers(struct worker_pool *pool)
/* Do we have too many workers and should some go away? */
static bool too_many_workers(struct worker_pool *pool)
{
bool managing = pool->flags & POOL_MANAGING_WORKERS;
bool managing = mutex_is_locked(&pool->manager_mutex);
int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
int nr_busy = pool->nr_workers - nr_idle;
@ -1655,14 +1655,12 @@ static bool maybe_destroy_workers(struct worker_pool *pool)
static bool manage_workers(struct worker *worker)
{
struct worker_pool *pool = worker->pool;
struct global_cwq *gcwq = pool->gcwq;
bool ret = false;
if (pool->flags & POOL_MANAGING_WORKERS)
if (!mutex_trylock(&pool->manager_mutex))
return ret;
pool->flags &= ~POOL_MANAGE_WORKERS;
pool->flags |= POOL_MANAGING_WORKERS;
/*
* Destroy and then create so that may_start_working() is true
@ -1671,15 +1669,7 @@ static bool manage_workers(struct worker *worker)
ret |= maybe_destroy_workers(pool);
ret |= maybe_create_worker(pool);
pool->flags &= ~POOL_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);
mutex_unlock(&pool->manager_mutex);
return ret;
}
@ -3255,6 +3245,24 @@ EXPORT_SYMBOL_GPL(work_busy);
* ----------------> RELEASE --------------
*/
/* claim manager positions of all pools */
static void gcwq_claim_management(struct global_cwq *gcwq)
{
struct worker_pool *pool;
for_each_worker_pool(pool, gcwq)
mutex_lock_nested(&pool->manager_mutex, pool - gcwq->pools);
}
/* release manager positions */
static void gcwq_release_management(struct global_cwq *gcwq)
{
struct worker_pool *pool;
for_each_worker_pool(pool, gcwq)
mutex_unlock(&pool->manager_mutex);
}
/**
* trustee_wait_event_timeout - timed event wait for trustee
* @cond: condition to wait for
@ -3304,16 +3312,6 @@ EXPORT_SYMBOL_GPL(work_busy);
__ret1 < 0 ? -1 : 0; \
})
static bool gcwq_is_managing_workers(struct global_cwq *gcwq)
{
struct worker_pool *pool;
for_each_worker_pool(pool, gcwq)
if (pool->flags & POOL_MANAGING_WORKERS)
return true;
return false;
}
static bool gcwq_has_idle_workers(struct global_cwq *gcwq)
{
struct worker_pool *pool;
@ -3336,15 +3334,8 @@ static int __cpuinit trustee_thread(void *__gcwq)
BUG_ON(gcwq->cpu != smp_processor_id());
gcwq_claim_management(gcwq);
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_is_managing_workers(gcwq));
BUG_ON(rc < 0);
/*
* We've claimed all manager positions. Make all workers unbound
@ -3352,12 +3343,9 @@ static int __cpuinit trustee_thread(void *__gcwq)
* 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) {
pool->flags |= POOL_MANAGING_WORKERS;
for_each_worker_pool(pool, gcwq)
list_for_each_entry(worker, &pool->idle_list, entry)
worker->flags |= WORKER_UNBOUND;
}
for_each_busy_worker(worker, i, pos, gcwq)
worker->flags |= WORKER_UNBOUND;
@ -3497,9 +3485,7 @@ static int __cpuinit trustee_thread(void *__gcwq)
work_color_to_flags(WORK_NO_COLOR));
}
/* relinquish manager role */
for_each_worker_pool(pool, gcwq)
pool->flags &= ~POOL_MANAGING_WORKERS;
gcwq_release_management(gcwq);
/* notify completion */
gcwq->trustee = NULL;
@ -3894,6 +3880,7 @@ static int __init init_workqueues(void)
setup_timer(&pool->mayday_timer, gcwq_mayday_timeout,
(unsigned long)pool);
mutex_init(&pool->manager_mutex);
ida_init(&pool->worker_ida);
}