Upgrade to 4.4.50-rt62

[kvmfornfv.git] / kernel / kernel / workqueue.c

diff --git a/kernel/kernel/workqueue.c b/kernel/kernel/workqueue.c
index efd1f58..d5b0f4f 100644 (file)
--- a/kernel/kernel/workqueue.c
+++ b/kernel/kernel/workqueue.c
@@ -683,6 +683,35 @@ static void set_work_pool_and_clear_pending(struct work_struct *work,
         */
        smp_wmb();
        set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT, 0);
+       /*
+        * The following mb guarantees that previous clear of a PENDING bit
+        * will not be reordered with any speculative LOADS or STORES from
+        * work->current_func, which is executed afterwards.  This possible
+        * reordering can lead to a missed execution on attempt to qeueue
+        * the same @work.  E.g. consider this case:
+        *
+        *   CPU#0                         CPU#1
+        *   ----------------------------  --------------------------------
+        *
+        * 1  STORE event_indicated
+        * 2  queue_work_on() {
+        * 3    test_and_set_bit(PENDING)
+        * 4 }                             set_..._and_clear_pending() {
+        * 5                                 set_work_data() # clear bit
+        * 6                                 smp_mb()
+        * 7                               work->current_func() {
+        * 8                                  LOAD event_indicated
+        *                                 }
+        *
+        * Without an explicit full barrier speculative LOAD on line 8 can
+        * be executed before CPU#0 does STORE on line 1.  If that happens,
+        * CPU#0 observes the PENDING bit is still set and new execution of
+        * a @work is not queued in a hope, that CPU#1 will eventually
+        * finish the queued @work.  Meanwhile CPU#1 does not see
+        * event_indicated is set, because speculative LOAD was executed
+        * before actual STORE.
+        */
+       smp_mb();
 }
 
 static void clear_work_data(struct work_struct *work)
@@ -1106,9 +1135,11 @@ static void put_pwq_unlocked(struct pool_workqueue *pwq)
                 * As both pwqs and pools are RCU protected, the
                 * following lock operations are safe.
                 */
+               rcu_read_lock();
                local_spin_lock_irq(pendingb_lock, &pwq->pool->lock);
                put_pwq(pwq);
                local_spin_unlock_irq(pendingb_lock, &pwq->pool->lock);
+               rcu_read_unlock();
        }
 }
 
@@ -4466,6 +4497,17 @@ static void rebind_workers(struct worker_pool *pool)
                                                  pool->attrs->cpumask) < 0);
 
        spin_lock_irq(&pool->lock);
+
+       /*
+        * XXX: CPU hotplug notifiers are weird and can call DOWN_FAILED
+        * w/o preceding DOWN_PREPARE.  Work around it.  CPU hotplug is
+        * being reworked and this can go away in time.
+        */
+       if (!(pool->flags & POOL_DISASSOCIATED)) {
+               spin_unlock_irq(&pool->lock);
+               return;
+       }
+
        pool->flags &= ~POOL_DISASSOCIATED;
 
        for_each_pool_worker(worker, pool) {