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workqueue: remove the confusing POOL_FREEZING

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Currently, the global freezing state is propagated to worker_pools via
POOL_FREEZING and then to each workqueue; however, the middle step -
propagation through worker_pools - can be skipped as long as one or
more max_active adjustments happens for each workqueue after the
update to the global state is visible.  The global workqueue freezing
state and the max_active adjustments during workqueue creation and
[un]freezing are serialized with wq_pool_mutex, so it's trivial to
guarantee that max_actives stay in sync with global freezing state.

POOL_FREEZING is unnecessary and makes the code more confusing and
complicates freeze_workqueues_begin() and thaw_workqueues() by
requiring them to walk through all pools.

Remove POOL_FREEZING and use workqueue_freezing directly instead.

tj: Description and comment updates.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Lai Jiangshan 2014-05-22 19:01:16 +08:00 • committed by Tejun Heo
parent 1037de36ed
commit 74b414ead1
1 changed files with 7 additions and 25 deletions
Download patch file Download diff file Expand all files Collapse all files

32
kernel/workqueue.c
View file

@ -69,7 +69,6 @@ enum {
* worker_attach_to_pool() is in progress. * worker_attach_to_pool() is in progress.
*/ */
POOL_DISASSOCIATED = 1 << 2, /* cpu can't serve workers */ POOL_DISASSOCIATED = 1 << 2, /* cpu can't serve workers */
POOL_FREEZING = 1 << 3, /* freeze in progress */
/* worker flags */ /* worker flags */
WORKER_DIE = 1 << 1, /* die die die */ WORKER_DIE = 1 << 1, /* die die die */
@ -3533,9 +3532,6 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
if (!pool || init_worker_pool(pool) < 0) if (!pool || init_worker_pool(pool) < 0)
goto fail; goto fail;
if (workqueue_freezing)
pool->flags |= POOL_FREEZING;
lockdep_set_subclass(&pool->lock, 1); /* see put_pwq() */ lockdep_set_subclass(&pool->lock, 1); /* see put_pwq() */
copy_workqueue_attrs(pool->attrs, attrs); copy_workqueue_attrs(pool->attrs, attrs);
@ -3642,7 +3638,12 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq)
spin_lock_irq(&pwq->pool->lock); spin_lock_irq(&pwq->pool->lock);
if (!freezable || !(pwq->pool->flags & POOL_FREEZING)) { /*
* During [un]freezing, the caller is responsible for ensuring that
* this function is called at least once after @workqueue_freezing
* is updated and visible.
*/
if (!freezable || !workqueue_freezing) {
pwq->max_active = wq->saved_max_active; pwq->max_active = wq->saved_max_active;
while (!list_empty(&pwq->delayed_works) && while (!list_empty(&pwq->delayed_works) &&
@ -4751,24 +4752,14 @@ EXPORT_SYMBOL_GPL(work_on_cpu);
*/ */
void freeze_workqueues_begin(void) void freeze_workqueues_begin(void)
{ {
struct worker_pool *pool;
struct workqueue_struct *wq; struct workqueue_struct *wq;
struct pool_workqueue *pwq; struct pool_workqueue *pwq;
int pi;
mutex_lock(&wq_pool_mutex); mutex_lock(&wq_pool_mutex);
WARN_ON_ONCE(workqueue_freezing); WARN_ON_ONCE(workqueue_freezing);
workqueue_freezing = true; workqueue_freezing = true;
/* set FREEZING */
for_each_pool(pool, pi) {
spin_lock_irq(&pool->lock);
WARN_ON_ONCE(pool->flags & POOL_FREEZING);
pool->flags |= POOL_FREEZING;
spin_unlock_irq(&pool->lock);
}
list_for_each_entry(wq, &workqueues, list) { list_for_each_entry(wq, &workqueues, list) {
mutex_lock(&wq->mutex); mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq) for_each_pwq(pwq, wq)
@ -4838,21 +4829,13 @@ void thaw_workqueues(void)
{ {
struct workqueue_struct *wq; struct workqueue_struct *wq;
struct pool_workqueue *pwq; struct pool_workqueue *pwq;
struct worker_pool *pool;
int pi;
mutex_lock(&wq_pool_mutex); mutex_lock(&wq_pool_mutex);
if (!workqueue_freezing) if (!workqueue_freezing)
goto out_unlock; goto out_unlock;
/* clear FREEZING */ workqueue_freezing = false;
for_each_pool(pool, pi) {
spin_lock_irq(&pool->lock);
WARN_ON_ONCE(!(pool->flags & POOL_FREEZING));
pool->flags &= ~POOL_FREEZING;
spin_unlock_irq(&pool->lock);
}
/* restore max_active and repopulate worklist */ /* restore max_active and repopulate worklist */
list_for_each_entry(wq, &workqueues, list) { list_for_each_entry(wq, &workqueues, list) {
@ -4862,7 +4845,6 @@ void thaw_workqueues(void)
mutex_unlock(&wq->mutex); mutex_unlock(&wq->mutex);
} }
workqueue_freezing = false;
out_unlock: out_unlock:
mutex_unlock(&wq_pool_mutex); mutex_unlock(&wq_pool_mutex);
} }