[3.13.y.z extended stable] Patch "workqueue: apply __WQ_ORDERED to create_singlethread_workqueue()" has been added to staging queue

Kamal Mostafa kamal at canonical.com
Thu Oct 9 20:51:40 UTC 2014

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

    workqueue: apply __WQ_ORDERED to create_singlethread_workqueue()

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:


This patch is scheduled to be released in version

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

For more information about the 3.13.y.z tree, see



>From c89a14f3f8244e0f9c7d81158aeae97e65f90b19 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj at kernel.org>
Date: Sat, 13 Sep 2014 04:14:30 +0900
Subject: workqueue: apply __WQ_ORDERED to create_singlethread_workqueue()

commit e09c2c295468476a239d13324ce9042ec4de05eb upstream.

create_singlethread_workqueue() is a compat interface for single
threaded workqueue which maps to ordered workqueue w/ rescuer in the
current implementation.  create_singlethread_workqueue() currently
implemented by invoking alloc_workqueue() w/ appropriate parameters.

8719dceae2f9 ("workqueue: reject adjusting max_active or applying
attrs to ordered workqueues") introduced __WQ_ORDERED to protect
ordered workqueues against dynamic attribute changes which can break
ordering guarantees but forgot to apply it to
create_singlethread_workqueue().  This in itself is okay as nobody
currently uses dynamic attribute change on workqueues created with

However, 4c16bd327c ("workqueue: implement NUMA affinity for unbound
workqueues") broke singlethreaded guarantee for ordered workqueues
through allocating a separate pool_workqueue on each NUMA node by
default.  A later change 8a2b75384444 ("workqueue: fix ordered
workqueues in NUMA setups") fixed it by allocating only one global
pool_workqueue if __WQ_ORDERED is set.

Combined, the __WQ_ORDERED omission in create_singlethread_workqueue()
became critical breaking its single threadedness and ordering

Let's make create_singlethread_workqueue() wrap
alloc_ordered_workqueue() instead so that it inherits __WQ_ORDERED and
can implicitly track future ordered_workqueue changes.

v2: I missed that __WQ_ORDERED now protects against pwq splitting
    across NUMA nodes and incorrectly described the patch as a
    nice-to-have fix to protect against future dynamic attribute
    usages.  Oleg pointed out that this is actually a critical
    breakage due to 8a2b75384444 ("workqueue: fix ordered workqueues
    in NUMA setups").

Signed-off-by: Tejun Heo <tj at kernel.org>
Reported-by: Mike Anderson <mike.anderson at us.ibm.com>
Cc: Oleg Nesterov <onestero at redhat.com>
Cc: Gustavo Luiz Duarte <gduarte at redhat.com>
Cc: Tomas Henzl <thenzl at redhat.com>
Fixes: 4c16bd327c ("workqueue: implement NUMA affinity for unbound workqueues")
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 include/linux/workqueue.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 594521b..eff358e 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -455,7 +455,7 @@ __alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,
 	alloc_workqueue("%s", WQ_FREEZABLE | WQ_UNBOUND | WQ_MEM_RECLAIM, \
 			1, (name))
 #define create_singlethread_workqueue(name)				\
-	alloc_workqueue("%s", WQ_UNBOUND | WQ_MEM_RECLAIM, 1, (name))
+	alloc_ordered_workqueue("%s", WQ_MEM_RECLAIM, name)

 extern void destroy_workqueue(struct workqueue_struct *wq);


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