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Message-Id: <1347124383-18723-3-git-send-email-laijs@cn.fujitsu.com>
Date: Sun, 9 Sep 2012 01:12:51 +0800
From: Lai Jiangshan <laijs@...fujitsu.com>
To: Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Cc: Lai Jiangshan <laijs@...fujitsu.com>
Subject: [PATCH 2/7 V6] workqueue: async idle rebinding
fix deadlock in rebind_workers()
Current idle_worker_rebind() has a bug.
idle_worker_rebind() path HOTPLUG path
online
rebind_workers()
wait_event(gcwq->rebind_hold)
woken up but no scheduled rebind_workers() returns
the same cpu offline
the same cpu online again
rebind_workers()
set WORKER_REBIND
scheduled,see the WORKER_REBIND
wait rebind_workers() clear it <--bug--> wait idle_worker_rebind()
rebound.
The two thread wait each other. It is bug.
This patch gives up to rebind idles synchronously. make them async instead.
To avoid to wrongly do local-wake-up, we add a exile-operation for
idle-worker-rebinding. When a idle worker is exiled, it will not queued
on @idle_list until it is rebound.
After we have exile-operation, the @nr_idle is not only the count of @idle_list,
but also exiled idle workers. so I check all the code, and make
them exile-operation aware. (too_many_workers())
exile-operation is also the core idea to rebind newly created worker.
(patch 9)
rebind_workers() become single pass and don't release gcwq->lock.
Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
kernel/workqueue.c | 100 +++++++++++++---------------------------------------
1 files changed, 25 insertions(+), 75 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 050b2a5..3dd7ce2 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -125,7 +125,6 @@ enum {
struct global_cwq;
struct worker_pool;
-struct idle_rebind;
/*
* The poor guys doing the actual heavy lifting. All on-duty workers
@@ -149,7 +148,6 @@ struct worker {
int id; /* I: worker id */
/* for rebinding worker to CPU */
- struct idle_rebind *idle_rebind; /* L: for idle worker */
struct work_struct rebind_work; /* L: for busy worker */
};
@@ -159,7 +157,9 @@ struct worker_pool {
struct list_head worklist; /* L: list of pending works */
int nr_workers; /* L: total number of workers */
- int nr_idle; /* L: currently idle ones */
+ int nr_idle; /* L: currently idle ones,
+ include ones in idle_list
+ and in doing rebind. */
struct list_head idle_list; /* X: list of idle workers */
struct timer_list idle_timer; /* L: worker idle timeout */
@@ -185,8 +185,6 @@ struct global_cwq {
struct worker_pool pools[NR_WORKER_POOLS];
/* normal and highpri pools */
-
- wait_queue_head_t rebind_hold; /* rebind hold wait */
} ____cacheline_aligned_in_smp;
/*
@@ -686,6 +684,10 @@ static bool too_many_workers(struct worker_pool *pool)
int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
int nr_busy = pool->nr_workers - nr_idle;
+ /* Is any idle home ? */
+ if (unlikely(list_empty(&pool->idle_list)))
+ return false;
+
return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy;
}
@@ -1608,28 +1610,20 @@ __acquires(&gcwq->lock)
}
}
-struct idle_rebind {
- int cnt; /* # workers to be rebound */
- struct completion done; /* all workers rebound */
-};
-
/*
- * Rebind an idle @worker to its CPU. During CPU onlining, this has to
- * happen synchronously for idle workers. worker_thread() will test
+ * Rebind an idle @worker to its CPU. worker_thread() will test
* %WORKER_REBIND before leaving idle and call this function.
*/
static void idle_worker_rebind(struct worker *worker)
{
struct global_cwq *gcwq = worker->pool->gcwq;
- /* CPU must be online at this point */
- WARN_ON(!worker_maybe_bind_and_lock(worker));
- if (!--worker->idle_rebind->cnt)
- complete(&worker->idle_rebind->done);
- spin_unlock_irq(&worker->pool->gcwq->lock);
+ if (worker_maybe_bind_and_lock(worker))
+ worker_clr_flags(worker, WORKER_UNBOUND);
- /* we did our part, wait for rebind_workers() to finish up */
- wait_event(gcwq->rebind_hold, !(worker->flags & WORKER_REBIND));
+ worker_clr_flags(worker, WORKER_REBIND);
+ list_add(&worker->entry, &worker->pool->idle_list);
+ spin_unlock_irq(&gcwq->lock);
}
/*
@@ -1656,29 +1650,22 @@ static void busy_worker_rebind_fn(struct work_struct *work)
* @gcwq->cpu is coming online. Rebind all workers to the CPU. Rebinding
* is different for idle and busy ones.
*
- * The idle ones should be rebound synchronously and idle rebinding should
- * be complete before any worker starts executing work items with
- * concurrency management enabled; otherwise, scheduler may oops trying to
- * wake up non-local idle worker from wq_worker_sleeping().
- *
- * This is achieved by repeatedly requesting rebinding until all idle
- * workers are known to have been rebound under @gcwq->lock and holding all
- * idle workers from becoming busy until idle rebinding is complete.
+ * The idle ones will be kicked out of the idle_list, and it will
+ * add itself back when it finish to rebind.
*
- * Once idle workers are rebound, busy workers can be rebound as they
- * finish executing their current work items. Queueing the rebind work at
- * the head of their scheduled lists is enough. Note that nr_running will
+ * The busy workers can be rebound as they finish executing
+ * their current work items. Queueing the rebind work at the head of
+ * their scheduled lists is enough. Note that nr_running will
* be properbly bumped as busy workers rebind.
*
- * On return, all workers are guaranteed to either be bound or have rebind
- * work item scheduled.
+ * On return, all workers are guaranteed to be rebound when they
+ * 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 idle_rebind idle_rebind;
struct worker_pool *pool;
- struct worker *worker;
+ struct worker *worker, *n;
struct hlist_node *pos;
int i;
@@ -1687,54 +1674,19 @@ static void rebind_workers(struct global_cwq *gcwq)
for_each_worker_pool(pool, gcwq)
lockdep_assert_held(&pool->manager_mutex);
- /*
- * Rebind idle workers. Interlocked both ways. We wait for
- * workers to rebind via @idle_rebind.done. Workers will wait for
- * us to finish up by watching %WORKER_REBIND.
- */
- init_completion(&idle_rebind.done);
-retry:
- idle_rebind.cnt = 1;
- INIT_COMPLETION(idle_rebind.done);
-
- /* set REBIND and kick idle ones, we'll wait for these later */
+ /* set REBIND and kick idle ones */
for_each_worker_pool(pool, gcwq) {
- list_for_each_entry(worker, &pool->idle_list, entry) {
- if (worker->flags & WORKER_REBIND)
- continue;
-
- /* morph UNBOUND to REBIND */
- worker->flags &= ~WORKER_UNBOUND;
+ list_for_each_entry_safe(worker, n, &pool->idle_list, entry) {
worker->flags |= WORKER_REBIND;
- idle_rebind.cnt++;
- worker->idle_rebind = &idle_rebind;
+ /* exile idle workers */
+ list_del_init(&worker->entry);
/* worker_thread() will call idle_worker_rebind() */
wake_up_process(worker->task);
}
}
- if (--idle_rebind.cnt) {
- spin_unlock_irq(&gcwq->lock);
- wait_for_completion(&idle_rebind.done);
- spin_lock_irq(&gcwq->lock);
- /* busy ones might have become idle while waiting, retry */
- goto retry;
- }
-
- /*
- * All idle workers are rebound and waiting for %WORKER_REBIND to
- * be cleared inside idle_worker_rebind(). Clear and release.
- * Clearing %WORKER_REBIND from this foreign context is safe
- * because these workers are still guaranteed to be idle.
- */
- for_each_worker_pool(pool, gcwq)
- list_for_each_entry(worker, &pool->idle_list, entry)
- worker->flags &= ~WORKER_REBIND;
-
- wake_up_all(&gcwq->rebind_hold);
-
/* rebind busy workers */
for_each_busy_worker(worker, i, pos, gcwq) {
struct work_struct *rebind_work = &worker->rebind_work;
@@ -3811,8 +3763,6 @@ static int __init init_workqueues(void)
mutex_init(&pool->manager_mutex);
ida_init(&pool->worker_ida);
}
-
- init_waitqueue_head(&gcwq->rebind_hold);
}
/* create the initial worker */
--
1.7.4.4
--
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