From 75ccf5950f828d53aebfd3a852283a00abf2c5bf Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Tue, 12 Mar 2013 11:30:04 -0700
Subject: [PATCH] workqueue: prepare flush_workqueue() for dynamic creation and
 destrucion of unbound pool_workqueues

Unbound pwqs (pool_workqueues) will be dynamically created and
destroyed with the scheduled unbound workqueue w/ custom attributes
support.  This patch synchronizes pwq linking and unlinking against
flush_workqueue() so that its operation isn't disturbed by pwqs coming
and going.

Linking and unlinking a pwq into wq->pwqs is now protected also by
wq->flush_mutex and a new pwq's work_color is initialized to
wq->work_color during linking.  This ensures that pwqs changes don't
disturb flush_workqueue() in progress and the new pwq's work coloring
stays in sync with the rest of the workqueue.

flush_mutex during unlinking isn't strictly necessary but it's simpler
to do it anyway.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
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