Merge branch 'for-4.13-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq

Pull workqueue fixes from Tejun Heo:
 "Two notable fixes.

   - While adding NUMA affinity support to unbound workqueues, the
     assumption that an unbound workqueue with max_active == 1 is
     ordered was broken.

     The plan was to use explicit alloc_ordered_workqueue() for those
     cases. Unfortunately, I forgot to update the documentation properly
     and we grew a handful of use cases which depend on that assumption.

     While we want to convert them to alloc_ordered_workqueue(), we
     don't really lose anything by enforcing ordered execution on
     unbound max_active == 1 workqueues and it doesn't make sense to
     risk subtle bugs. Restore the assumption.

   - Workqueue assumes that CPU <-> NUMA node mapping remains static.

     This is a general assumption - we don't have any synchronization
     mechanism around CPU <-> node mapping. Unfortunately, powerpc may
     change the mapping dynamically leading to crashes. Michael added a
     workaround so that we at least don't crash while powerpc hotplug
     code gets updated"

* 'for-4.13-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
  workqueue: Work around edge cases for calc of pool's cpumask
  workqueue: implicit ordered attribute should be overridable
  workqueue: restore WQ_UNBOUND/max_active==1 to be ordered

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index c102ef65cb64a94269b950ff09c47d90bbc2d315..db6dc9dc0482bf1299c010f54873f2ae36a4684e 100644 (file)
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -323,6 +323,7 @@ enum {
 
        __WQ_DRAINING           = 1 << 16, /* internal: workqueue is draining */
        __WQ_ORDERED            = 1 << 17, /* internal: workqueue is ordered */
+       __WQ_ORDERED_EXPLICIT   = 1 << 18, /* internal: alloc_ordered_workqueue() */
        __WQ_LEGACY             = 1 << 18, /* internal: create*_workqueue() */
 
        WQ_MAX_ACTIVE           = 512,    /* I like 512, better ideas? */
@@ -422,7 +423,8 @@ __alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,
  * Pointer to the allocated workqueue on success, %NULL on failure.
  */
 #define alloc_ordered_workqueue(fmt, flags, args...)                   \
-       alloc_workqueue(fmt, WQ_UNBOUND | __WQ_ORDERED | (flags), 1, ##args)
+       alloc_workqueue(fmt, WQ_UNBOUND | __WQ_ORDERED |                \
+                       __WQ_ORDERED_EXPLICIT | (flags), 1, ##args)
 
 #define create_workqueue(name)                                         \
        alloc_workqueue("%s", __WQ_LEGACY | WQ_MEM_RECLAIM, 1, (name))

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a86688fabc55c4a4ec2bad843f6dc1e0e411f2d1..ca937b0c3a968f247a227d68812c9062fb4916c5 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3577,6 +3577,13 @@ static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,
 
        /* yeap, return possible CPUs in @node that @attrs wants */
        cpumask_and(cpumask, attrs->cpumask, wq_numa_possible_cpumask[node]);
+
+       if (cpumask_empty(cpumask)) {
+               pr_warn_once("WARNING: workqueue cpumask: online intersect > "
+                               "possible intersect\n");
+               return false;
+       }
+
        return !cpumask_equal(cpumask, attrs->cpumask);
 
 use_dfl:
@@ -3744,8 +3751,12 @@ static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
                return -EINVAL;
 
        /* creating multiple pwqs breaks ordering guarantee */
-       if (WARN_ON((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs)))
-               return -EINVAL;
+       if (!list_empty(&wq->pwqs)) {
+               if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
+                       return -EINVAL;
+
+               wq->flags &= ~__WQ_ORDERED;
+       }
 
        ctx = apply_wqattrs_prepare(wq, attrs);
        if (!ctx)
@@ -3929,6 +3940,16 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
        struct workqueue_struct *wq;
        struct pool_workqueue *pwq;
 
+       /*
+        * Unbound && max_active == 1 used to imply ordered, which is no
+        * longer the case on NUMA machines due to per-node pools.  While
+        * alloc_ordered_workqueue() is the right way to create an ordered
+        * workqueue, keep the previous behavior to avoid subtle breakages
+        * on NUMA.
+        */
+       if ((flags & WQ_UNBOUND) && max_active == 1)
+               flags |= __WQ_ORDERED;
+
        /* see the comment above the definition of WQ_POWER_EFFICIENT */
        if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
                flags |= WQ_UNBOUND;
@@ -4119,13 +4140,14 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
        struct pool_workqueue *pwq;
 
        /* disallow meddling with max_active for ordered workqueues */
-       if (WARN_ON(wq->flags & __WQ_ORDERED))
+       if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
                return;
 
        max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);
 
        mutex_lock(&wq->mutex);
 
+       wq->flags &= ~__WQ_ORDERED;
        wq->saved_max_active = max_active;
 
        for_each_pwq(pwq, wq)
@@ -5253,7 +5275,7 @@ int workqueue_sysfs_register(struct workqueue_struct *wq)
         * attributes breaks ordering guarantee.  Disallow exposing ordered
         * workqueues.
         */
-       if (WARN_ON(wq->flags & __WQ_ORDERED))
+       if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
                return -EINVAL;
 
        wq->wq_dev = wq_dev = kzalloc(sizeof(*wq_dev), GFP_KERNEL);