workqueue: Fix spurious sanity check failures in destroy_workqueue()

commit def98c84b6cdf2eeea19ec5736e90e316df5206b upstream.

Before actually destrying a workqueue, destroy_workqueue() checks
whether it's actually idle.  If it isn't, it prints out a bunch of
warning messages and leaves the workqueue dangling.  It unfortunately
has a couple issues.

* Mayday list queueing increments pwq's refcnts which gets detected as
  busy and fails the sanity checks.  However, because mayday list
  queueing is asynchronous, this condition can happen without any
  actual work items left in the workqueue.

* Sanity check failure leaves the sysfs interface behind too which can
  lead to init failure of newer instances of the workqueue.

This patch fixes the above two by

* If a workqueue has a rescuer, disable and kill the rescuer before
  sanity checks.  Disabling and killing is guaranteed to flush the
  existing mayday list.

* Remove sysfs interface before sanity checks.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Marcin Pawlowski <mpawlowski@fb.com>
Reported-by: "Williams, Gerald S" <gerald.s.williams@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1961dd408bc59eb5de7fb338d5d949c75b1154a5..7d7f0941aaa9c3ff926ba48624b17ae28ba6df03 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4031,9 +4031,28 @@ void destroy_workqueue(struct workqueue_struct *wq)
        struct pool_workqueue *pwq;
        int node;
 
+       /*
+        * Remove it from sysfs first so that sanity check failure doesn't
+        * lead to sysfs name conflicts.
+        */
+       workqueue_sysfs_unregister(wq);
+
        /* drain it before proceeding with destruction */
        drain_workqueue(wq);
 
+       /* kill rescuer, if sanity checks fail, leave it w/o rescuer */
+       if (wq->rescuer) {
+               struct worker *rescuer = wq->rescuer;
+
+               /* this prevents new queueing */
+               spin_lock_irq(&wq_mayday_lock);
+               wq->rescuer = NULL;
+               spin_unlock_irq(&wq_mayday_lock);
+
+               /* rescuer will empty maydays list before exiting */
+               kthread_stop(rescuer->task);
+       }
+
        /* sanity checks */
        mutex_lock(&wq->mutex);
        for_each_pwq(pwq, wq) {
@@ -4063,11 +4082,6 @@ void destroy_workqueue(struct workqueue_struct *wq)
        list_del_rcu(&wq->list);
        mutex_unlock(&wq_pool_mutex);
 
-       workqueue_sysfs_unregister(wq);
-
-       if (wq->rescuer)
-               kthread_stop(wq->rescuer->task);
-
        if (!(wq->flags & WQ_UNBOUND)) {
                /*
                 * The base ref is never dropped on per-cpu pwqs.  Directly