[PATCH wq/for-7.4 2/2] workqueue: derive the standard attrs from the workqueue flags

[Breno Leitao <leitao@debian.org>]

alloc_and_link_pwqs() picks one of three static attrs arrays indexed by
WQ_HIGHPRI, and branches to a separate apply_workqueue_attrs_locked()
call for percpu, ordered and unbound workqueues. The arrays differ only
in the nice level and the ordered bit, which the flags already say.

Build the attrs from the flags instead. alloc_wq_std_attrs() sets nice
for WQ_HIGHPRI and ordered for __WQ_ORDERED, which collapses the three
branches into one call and drops the three arrays along with their
workqueue_init_early() loop.

The ordering WARN now sits behind its own __WQ_ORDERED test rather than
the unbound branch. __WQ_ORDERED is internal and every macro that sets it
pairs it with WQ_UNBOUND, so the WARN covers the same workqueues as
before.

The attrs are allocated per creation now. apply_wqattrs_prepare() already
allocates one on the same path, including in workqueue_init_early(), so
that is not a new constraint, and it only copies what it is given, so the
caller can free them once apply_workqueue_attrs_locked() returns.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 kernel/workqueue.c | 76 +++++++++++++++++++++++-------------------------------
 1 file changed, 32 insertions(+), 44 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 8232a60e107cf7..39187f424c34e7 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -533,15 +533,6 @@ static DEFINE_IDR(worker_pool_idr);	/* PR: idr of all pools */
 /* PL: hash of all unbound pools keyed by pool->attrs */
 static DEFINE_HASHTABLE(unbound_pool_hash, UNBOUND_POOL_HASH_ORDER);
 
-/* I: attributes used when instantiating standard unbound pools on demand */
-static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS];
-
-/* I: attributes used when instantiating ordered pools on demand */
-static struct workqueue_attrs *ordered_wq_attrs[NR_STD_WORKER_POOLS];
-
-/* I: attributes of percpu workqueues, which are backed by the static pools */
-static struct workqueue_attrs *percpu_std_wq_attrs[NR_STD_WORKER_POOLS];
-
 /*
  * I: kthread_worker to release pwq's. pwq release needs to be bounced to a
  * process context while holding a pool lock. Bounce to a dedicated kthread
@@ -5920,9 +5911,27 @@ static void unbound_wq_update_pwq(struct workqueue_struct *wq, int cpu)
 	put_pwq_unlocked(old_pwq);
 }
 
+/* the attrs @wq asked for, as spelled by its flags */
+static struct workqueue_attrs *alloc_wq_std_attrs(struct workqueue_struct *wq)
+{
+	struct workqueue_attrs *attrs;
+
+	attrs = alloc_workqueue_attrs();
+	if (!attrs)
+		return NULL;
+
+	if (wq->flags & WQ_HIGHPRI)
+		attrs->nice = HIGHPRI_NICE_LEVEL;
+
+	if (wq->flags & __WQ_ORDERED)
+		attrs->ordered = true;
+
+	return attrs;
+}
+
 static int alloc_and_link_pwqs(struct workqueue_struct *wq)
 {
-	bool highpri = wq->flags & WQ_HIGHPRI;
+	struct workqueue_attrs *attrs;
 	int ret;
 
 	lockdep_assert_held(&wq_pool_mutex);
@@ -5931,23 +5940,24 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
 	if (!wq->cpu_pwq)
 		goto enomem;
 
-	if (!(wq->flags & WQ_UNBOUND)) {
-		ret = apply_workqueue_attrs_locked(wq, percpu_std_wq_attrs[highpri]);
-	} else if (wq->flags & __WQ_ORDERED) {
-		struct pool_workqueue *dfl_pwq;
+	attrs = alloc_wq_std_attrs(wq);
+	if (!attrs)
+		goto enomem;
+
+	ret = apply_workqueue_attrs_locked(wq, attrs);
+	free_workqueue_attrs(attrs);
+	if (ret)
+		goto enomem;
+
+	if (wq->flags & __WQ_ORDERED) {
+		struct pool_workqueue *dfl_pwq = rcu_access_pointer(wq->dfl_pwq);
 
-		ret = apply_workqueue_attrs_locked(wq, ordered_wq_attrs[highpri]);
 		/* there should only be single pwq for ordering guarantee */
-		dfl_pwq = rcu_access_pointer(wq->dfl_pwq);
-		WARN(!ret && (wq->pwqs.next != &dfl_pwq->pwqs_node ||
-			      wq->pwqs.prev != &dfl_pwq->pwqs_node),
+		WARN(wq->pwqs.next != &dfl_pwq->pwqs_node ||
+		     wq->pwqs.prev != &dfl_pwq->pwqs_node,
 		     "ordering guarantee broken for workqueue %s\n", wq->name);
-	} else {
-		ret = apply_workqueue_attrs_locked(wq, unbound_std_wq_attrs[highpri]);
 	}
 
-	if (ret)
-		goto enomem;
 	return 0;
 
 enomem:
@@ -8378,28 +8388,6 @@ void __init workqueue_init_early(void)
 			init_cpu_worker_pool(pool, cpu, std_nice[i++]);
 	}
 
-	/* create default unbound, ordered and percpu wq attrs */
-	for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
-		struct workqueue_attrs *attrs;
-
-		BUG_ON(!(attrs = alloc_workqueue_attrs()));
-		attrs->nice = std_nice[i];
-		unbound_std_wq_attrs[i] = attrs;
-
-		/*
-		 * An ordered wq should have only one pwq as ordering is
-		 * guaranteed by max_active which is enforced by pwqs.
-		 */
-		BUG_ON(!(attrs = alloc_workqueue_attrs()));
-		attrs->nice = std_nice[i];
-		attrs->ordered = true;
-		ordered_wq_attrs[i] = attrs;
-
-		BUG_ON(!(attrs = alloc_workqueue_attrs()));
-		attrs->nice = std_nice[i];
-		percpu_std_wq_attrs[i] = attrs;
-	}
-
 	system_wq = alloc_workqueue("events", WQ_PERCPU | __WQ_DEPRECATED, 0);
 	system_percpu_wq = alloc_workqueue("events", WQ_PERCPU, 0);
 	system_highpri_wq = alloc_workqueue("events_highpri",

-- 
2.53.0-Meta