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From:   Bob Liu <bob.liu@oracle.com>
To:     linux-kernel@vger.kernel.org
Cc:     tj@kernel.org, martin.petersen@oracle.com,
        linux-scsi@vger.kernel.org, open-iscsi@googlegroups.com,
        lduncan@suse.com, michael.christie@oracle.com,
        Bob Liu <bob.liu@oracle.com>
Subject: [PATCH 1/2] workqueue: don't always set __WQ_ORDERED implicitly
Date:   Thu, 11 Jun 2020 18:07:16 +0800
Message-Id: <20200611100717.27506-1-bob.liu@oracle.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Current code always set 'Unbound && max_active == 1' workqueues to ordered
implicitly, while this may be not an expected behaviour for some use cases.

E.g some scsi and iscsi workqueues(unbound && max_active = 1) want to be bind
to different cpu so as to get better isolation, but their cpumask can't be
changed because WQ_ORDERED is set implicitly.

This patch adds a flag __WQ_ORDERED_DISABLE and also
create_singlethread_workqueue_noorder() to offer an new option.

Signed-off-by: Bob Liu <bob.liu@oracle.com>
---
 include/linux/workqueue.h | 4 ++++
 kernel/workqueue.c        | 4 +++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index e48554e..4c86913 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -344,6 +344,7 @@ enum {
 	__WQ_ORDERED		= 1 << 17, /* internal: workqueue is ordered */
 	__WQ_LEGACY		= 1 << 18, /* internal: create*_workqueue() */
 	__WQ_ORDERED_EXPLICIT	= 1 << 19, /* internal: alloc_ordered_workqueue() */
+	__WQ_ORDERED_DISABLE	= 1 << 20, /* internal: don't set __WQ_ORDERED implicitly */
 
 	WQ_MAX_ACTIVE		= 512,	  /* I like 512, better ideas? */
 	WQ_MAX_UNBOUND_PER_CPU	= 4,	  /* 4 * #cpus for unbound wq */
@@ -433,6 +434,9 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 #define create_singlethread_workqueue(name)				\
 	alloc_ordered_workqueue("%s", __WQ_LEGACY | WQ_MEM_RECLAIM, name)
 
+#define create_singlethread_workqueue_noorder(name)			\
+	alloc_workqueue("%s", WQ_SYSFS | __WQ_LEGACY | WQ_MEM_RECLAIM | \
+			WQ_UNBOUND | __WQ_ORDERED_DISABLE, 1, (name))
 extern void destroy_workqueue(struct workqueue_struct *wq);
 
 struct workqueue_attrs *alloc_workqueue_attrs(void);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4e01c44..2167013 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4237,7 +4237,9 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 	 * on NUMA.
 	 */
 	if ((flags & WQ_UNBOUND) && max_active == 1)
-		flags |= __WQ_ORDERED;
+		/* the caller may don't want __WQ_ORDERED to be set implicitly. */
+		if (!(flags & __WQ_ORDERED_DISABLE))
+			flags |= __WQ_ORDERED;
 
 	/* see the comment above the definition of WQ_POWER_EFFICIENT */
 	if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
-- 
2.9.5