Current idle_worker_rebind() has a bug.
Worker thread: The seconed CPU_ONLINE thread
idle_worker_rebind()
wait_event(gcwq->rebind_hold)
test for WORKER_REBIND and fails
sleeping...
#the first CPU_ONLINE is wokenup,
#finish its later work and gone.
this thread is also wokenup, but it is
not scheduled, it is still sleeping
sleeping...
#the cpu is offline again
#the cpu is online again,
#the online code do notify(CPU_ONLINE) call rebind_workers()
#I name this is the seconed CPU_ONLINE set WORKER_REBIND to idle
workers
#thread, see the right. .
.
this thread is finally scheduled, .
sees the WORKER_REBIND is not cleared, .
go to sleep again waiting for (another) .
rebind_workers() to wake up me. <--bug-> waiting for the idles' ACK.
The two thread wait each other. It is bug.
This fix:
The idle_worker_rebind() don't wait on rebind_hold, it waits on manager_mutex
instead. When mutex_lock(manager_mutex) returns, the idles know that
the corresponding rebind_workers() is finish up, the idle_worker_rebind() can
returns.
This fix has an advantage: WORKER_REBIND is not used for wait_event(),
so we can clear it in idle_worker_rebind().(next patch)
Signed-off-by: Lai Jiangshan <la...@cn.fujitsu.com>
---
kernel/workqueue.c | 13 +++----------
1 files changed, 3 insertions(+), 10 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 692d976..5872c31 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -184,8 +184,6 @@ struct global_cwq {
/* L: hash of busy workers */
struct worker_pool pools[2]; /* normal and highpri pools */
-
- wait_queue_head_t rebind_hold; /* rebind hold wait */
} ____cacheline_aligned_in_smp;
/*
@@ -1316,8 +1314,6 @@ struct idle_rebind {
*/
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)
@@ -1325,7 +1321,8 @@ static void idle_worker_rebind(struct worker *worker)
spin_unlock_irq(&worker->pool->gcwq->lock);
/* we did our part, wait for rebind_workers() to finish up */
- wait_event(gcwq->rebind_hold, !(worker->flags & WORKER_REBIND));
+ mutex_lock(&worker->pool->manager_mutex);
+ mutex_unlock(&worker->pool->manager_mutex);
}
/*
@@ -1386,7 +1383,7 @@ static void rebind_workers(struct global_cwq *gcwq)
/*
* 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.
+ * us to finish up by competing on pool->manager_mutex.
*/
init_completion(&idle_rebind.done);
retry:
@@ -1429,8 +1426,6 @@ retry:
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;
@@ -3722,8 +3717,6 @@ 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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