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Commit 75ccf595 authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
parent 8864b4e5

kernel/workqueue.c

+23 −2
Original line number Diff line number Diff line
@@ -122,6 +122,9 @@ enum { 
 * W: workqueue_lock protected.

 *

 * R: workqueue_lock protected for writes.  Sched-RCU protected for reads.

 *

 * FR: wq->flush_mutex and workqueue_lock protected for writes.  Sched-RCU

 *     protected for reads.

 */



/* struct worker is defined in workqueue_internal.h */
@@ -185,7 +188,7 @@ struct pool_workqueue { 
	int			nr_active;	/* L: nr of active works */

	int			max_active;	/* L: max active works */

	struct list_head	delayed_works;	/* L: delayed works */

	struct list_head	pwqs_node;	/* R: node on wq->pwqs */

	struct list_head	pwqs_node;	/* FR: node on wq->pwqs */

	struct list_head	mayday_node;	/* W: node on wq->maydays */



	/*
@@ -214,7 +217,7 @@ struct wq_flusher { 
struct workqueue_struct {

	unsigned int		flags;		/* W: WQ_* flags */

	struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwq's */

	struct list_head	pwqs;		/* R: all pwqs of this wq */

	struct list_head	pwqs;		/* FR: all pwqs of this wq */

	struct list_head	list;		/* W: list of all workqueues */



	struct mutex		flush_mutex;	/* protects wq flushing */
@@ -3402,9 +3405,16 @@ static void pwq_unbound_release_workfn(struct work_struct *work) 
	if (WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND)))

		return;



	/*

	 * Unlink @pwq.  Synchronization against flush_mutex isn't strictly

	 * necessary on release but do it anyway.  It's easier to verify

	 * and consistent with the linking path.

	 */

	mutex_lock(&wq->flush_mutex);

	spin_lock_irq(&workqueue_lock);

	list_del_rcu(&pwq->pwqs_node);

	spin_unlock_irq(&workqueue_lock);

	mutex_unlock(&wq->flush_mutex);



	put_unbound_pool(pool);

	call_rcu_sched(&pwq->rcu, rcu_free_pwq);
@@ -3432,7 +3442,18 @@ static void init_and_link_pwq(struct pool_workqueue *pwq, 
	INIT_LIST_HEAD(&pwq->mayday_node);

	INIT_WORK(&pwq->unbound_release_work, pwq_unbound_release_workfn);



	/*

	 * Link @pwq and set the matching work_color.  This is synchronized

	 * with flush_mutex to avoid confusing flush_workqueue().

	 */

	mutex_lock(&wq->flush_mutex);

	spin_lock_irq(&workqueue_lock);



	pwq->work_color = wq->work_color;

	list_add_tail_rcu(&pwq->pwqs_node, &wq->pwqs);



	spin_unlock_irq(&workqueue_lock);

	mutex_unlock(&wq->flush_mutex);

}



static int alloc_and_link_pwqs(struct workqueue_struct *wq)