workqueue: Fix spurious sanity check failures in destroy_workqueue()

BugLink: https://bugs.launchpad.net/bugs/1856869
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>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 601d61150b65de35d5b27cddb87462ff943ca52c..8a16beace63f8650e2a4a31bb66e6f850d3bb59b 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4316,9 +4316,28 @@ 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) {
@@ -4350,11 +4369,6 @@ 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)) {
                wq_unregister_lockdep(wq);
                /*