[3.11.y.z extended stable] Patch "workqueue: fix ordered workqueues in NUMA setups" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    workqueue: fix ordered workqueues in NUMA setups

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From b099fa4a57b42c11adb70f144fb69e8a408474bd Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj at kernel.org>
Date: Thu, 5 Sep 2013 12:30:04 -0400
Subject: workqueue: fix ordered workqueues in NUMA setups

commit 8a2b75384444488fc4f2cbb9f0921b6a0794838f upstream.

An ordered workqueue implements execution ordering by using single
pool_workqueue with max_active == 1.  On a given pool_workqueue, work
items are processed in FIFO order and limiting max_active to 1
enforces the queued work items to be processed one by one.

Unfortunately, 4c16bd327c ("workqueue: implement NUMA affinity for
unbound workqueues") accidentally broke this guarantee by applying
NUMA affinity to ordered workqueues too.  On NUMA setups, an ordered
workqueue would end up with separate pool_workqueues for different
nodes.  Each pool_workqueue still limits max_active to 1 but multiple
work items may be executed concurrently and out of order depending on
which node they are queued to.

Fix it by using dedicated ordered_wq_attrs[] when creating ordered
workqueues.  The new attrs match the unbound ones except that no_numa
is always set thus forcing all NUMA nodes to share the default
pool_workqueue.

While at it, add sanity check in workqueue creation path which
verifies that an ordered workqueues has only the default
pool_workqueue.

Signed-off-by: Tejun Heo <tj at kernel.org>
Reported-by: Libin <huawei.libin at huawei.com>
Cc: Lai Jiangshan <laijs at cn.fujitsu.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/workqueue.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e93f7b9..4235d5e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -304,6 +304,9 @@ 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];
+
 struct workqueue_struct *system_wq __read_mostly;
 EXPORT_SYMBOL(system_wq);
 struct workqueue_struct *system_highpri_wq __read_mostly;
@@ -4077,7 +4080,7 @@ out_unlock:
 static int alloc_and_link_pwqs(struct workqueue_struct *wq)
 {
 	bool highpri = wq->flags & WQ_HIGHPRI;
-	int cpu;
+	int cpu, ret;

 	if (!(wq->flags & WQ_UNBOUND)) {
 		wq->cpu_pwqs = alloc_percpu(struct pool_workqueue);
@@ -4097,6 +4100,13 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
 			mutex_unlock(&wq->mutex);
 		}
 		return 0;
+	} else if (wq->flags & __WQ_ORDERED) {
+		ret = apply_workqueue_attrs(wq, ordered_wq_attrs[highpri]);
+		/* there should only be single pwq for ordering guarantee */
+		WARN(!ret && (wq->pwqs.next != &wq->dfl_pwq->pwqs_node ||
+			      wq->pwqs.prev != &wq->dfl_pwq->pwqs_node),
+		     "ordering guarantee broken for workqueue %s\n", wq->name);
+		return ret;
 	} else {
 		return apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]);
 	}
@@ -5019,13 +5029,23 @@ static int __init init_workqueues(void)
 		}
 	}

-	/* create default unbound wq attrs */
+	/* create default unbound and ordered wq attrs */
 	for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
 		struct workqueue_attrs *attrs;

 		BUG_ON(!(attrs = alloc_workqueue_attrs(GFP_KERNEL)));
 		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.
+		 * Turn off NUMA so that dfl_pwq is used for all nodes.
+		 */
+		BUG_ON(!(attrs = alloc_workqueue_attrs(GFP_KERNEL)));
+		attrs->nice = std_nice[i];
+		attrs->no_numa = true;
+		ordered_wq_attrs[i] = attrs;
 	}

 	system_wq = alloc_workqueue("events", 0, 0);
--
1.8.3.2