workqueue: implicit ordered attribute should be overridable

5c0338c68706 ("workqueue: restore WQ_UNBOUND/max_active==1 to be
ordered") automatically enabled ordered attribute for unbound
workqueues w/ max_active == 1.  Because ordered workqueues reject
max_active and some attribute changes, this implicit ordered mode
broke cases where the user creates an unbound workqueue w/ max_active
== 1 and later explicitly changes the related attributes.

This patch distinguishes explicit and implicit ordered setting and
overrides from attribute changes if implict.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 5c0338c68706 ("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 abe4a4971c246ded51a0d81c53b714de97f61be9..7146ea70a62d124295feb36b9c3631279fffd365 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3744,8 +3744,12 @@ 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)
@@ -4129,13 +4133,14 @@ 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)
@@ -5263,7 +5268,7 @@ 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);