From: Tejun Heo tj@kernel.org
[ Upstream commit a045a272d887575da17ad86d6573e82871b50c27 ]
max_active is a workqueue-wide setting and the configured value is stored in wq->saved_max_active; however, the effective value was stored in pwq->max_active. While this is harmless, it makes max_active update process more complicated and gets in the way of the planned max_active semantic updates for unbound workqueues.
This patches moves pwq->max_active to wq->max_active. This simplifies the code and makes freezing and noop max_active updates cheaper too. No user-visible behavior change is intended.
As wq->max_active is updated while holding wq mutex but read without any locking, it now uses WRITE/READ_ONCE(). A new locking locking rule WO is added for it.
v2: wq->max_active now uses WRITE/READ_ONCE() as suggested by Lai.
Signed-off-by: Tejun Heo tj@kernel.org Reviewed-by: Lai Jiangshan jiangshanlai@gmail.com Stable-dep-of: 5797b1c18919 ("workqueue: Implement system-wide nr_active enforcement for unbound workqueues") Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/workqueue.c | 133 ++++++++++++++++++++++----------------------- 1 file changed, 66 insertions(+), 67 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 1c72a616b9888..f67eb40203ffc 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -143,6 +143,9 @@ enum { * * WR: wq->mutex protected for writes. RCU protected for reads. * + * WO: wq->mutex protected for writes. Updated with WRITE_ONCE() and can be read + * with READ_ONCE() without locking. + * * MD: wq_mayday_lock protected. * * WD: Used internally by the watchdog. @@ -250,7 +253,6 @@ struct pool_workqueue { * is marked with WORK_STRUCT_INACTIVE iff it is in pwq->inactive_works. */ int nr_active; /* L: nr of active works */ - int max_active; /* L: max active works */ struct list_head inactive_works; /* L: inactive works */ struct list_head pwqs_node; /* WR: node on wq->pwqs */ struct list_head mayday_node; /* MD: node on wq->maydays */ @@ -298,7 +300,8 @@ struct workqueue_struct { struct worker *rescuer; /* MD: rescue worker */
int nr_drainers; /* WQ: drain in progress */ - int saved_max_active; /* WQ: saved pwq max_active */ + int max_active; /* WO: max active works */ + int saved_max_active; /* WQ: saved max_active */
struct workqueue_attrs *unbound_attrs; /* PW: only for unbound wqs */ struct pool_workqueue *dfl_pwq; /* PW: only for unbound wqs */ @@ -1486,7 +1489,7 @@ static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, unsigned long work_ pwq->nr_active--; if (!list_empty(&pwq->inactive_works)) { /* one down, submit an inactive one */ - if (pwq->nr_active < pwq->max_active) + if (pwq->nr_active < READ_ONCE(pwq->wq->max_active)) pwq_activate_first_inactive(pwq); } } @@ -1787,7 +1790,13 @@ static void __queue_work(int cpu, struct workqueue_struct *wq, pwq->nr_in_flight[pwq->work_color]++; work_flags = work_color_to_flags(pwq->work_color);
- if (likely(pwq->nr_active < pwq->max_active)) { + /* + * Limit the number of concurrently active work items to max_active. + * @work must also queue behind existing inactive work items to maintain + * ordering when max_active changes. See wq_adjust_max_active(). + */ + if (list_empty(&pwq->inactive_works) && + pwq->nr_active < READ_ONCE(pwq->wq->max_active)) { if (list_empty(&pool->worklist)) pool->watchdog_ts = jiffies;
@@ -4136,50 +4145,6 @@ static void pwq_release_workfn(struct kthread_work *work) } }
-/** - * pwq_adjust_max_active - update a pwq's max_active to the current setting - * @pwq: target pool_workqueue - * - * If @pwq isn't freezing, set @pwq->max_active to the associated - * workqueue's saved_max_active and activate inactive work items - * accordingly. If @pwq is freezing, clear @pwq->max_active to zero. - */ -static void pwq_adjust_max_active(struct pool_workqueue *pwq) -{ - struct workqueue_struct *wq = pwq->wq; - bool freezable = wq->flags & WQ_FREEZABLE; - unsigned long flags; - - /* for @wq->saved_max_active */ - lockdep_assert_held(&wq->mutex); - - /* fast exit for non-freezable wqs */ - if (!freezable && pwq->max_active == wq->saved_max_active) - return; - - /* this function can be called during early boot w/ irq disabled */ - raw_spin_lock_irqsave(&pwq->pool->lock, flags); - - /* - * 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; - - while (!list_empty(&pwq->inactive_works) && - pwq->nr_active < pwq->max_active) - pwq_activate_first_inactive(pwq); - - kick_pool(pwq->pool); - } else { - pwq->max_active = 0; - } - - raw_spin_unlock_irqrestore(&pwq->pool->lock, flags); -} - /* initialize newly allocated @pwq which is associated with @wq and @pool */ static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq, struct worker_pool *pool) @@ -4212,9 +4177,6 @@ static void link_pwq(struct pool_workqueue *pwq) /* set the matching work_color */ pwq->work_color = wq->work_color;
- /* sync max_active to the current setting */ - pwq_adjust_max_active(pwq); - /* link in @pwq */ list_add_rcu(&pwq->pwqs_node, &wq->pwqs); } @@ -4665,6 +4627,52 @@ static int init_rescuer(struct workqueue_struct *wq) return 0; }
+/** + * wq_adjust_max_active - update a wq's max_active to the current setting + * @wq: target workqueue + * + * If @wq isn't freezing, set @wq->max_active to the saved_max_active and + * activate inactive work items accordingly. If @wq is freezing, clear + * @wq->max_active to zero. + */ +static void wq_adjust_max_active(struct workqueue_struct *wq) +{ + struct pool_workqueue *pwq; + + lockdep_assert_held(&wq->mutex); + + if ((wq->flags & WQ_FREEZABLE) && workqueue_freezing) { + WRITE_ONCE(wq->max_active, 0); + return; + } + + if (wq->max_active == wq->saved_max_active) + return; + + /* + * Update @wq->max_active and then kick inactive work items if more + * active work items are allowed. This doesn't break work item ordering + * because new work items are always queued behind existing inactive + * work items if there are any. + */ + WRITE_ONCE(wq->max_active, wq->saved_max_active); + + for_each_pwq(pwq, wq) { + unsigned long flags; + + /* this function can be called during early boot w/ irq disabled */ + raw_spin_lock_irqsave(&pwq->pool->lock, flags); + + while (!list_empty(&pwq->inactive_works) && + pwq->nr_active < wq->max_active) + pwq_activate_first_inactive(pwq); + + kick_pool(pwq->pool); + + raw_spin_unlock_irqrestore(&pwq->pool->lock, flags); + } +} + __printf(1, 4) struct workqueue_struct *alloc_workqueue(const char *fmt, unsigned int flags, @@ -4672,7 +4680,6 @@ struct workqueue_struct *alloc_workqueue(const char *fmt, { va_list args; struct workqueue_struct *wq; - struct pool_workqueue *pwq; int len;
/* @@ -4711,6 +4718,7 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
/* init wq */ wq->flags = flags; + wq->max_active = max_active; wq->saved_max_active = max_active; mutex_init(&wq->mutex); atomic_set(&wq->nr_pwqs_to_flush, 0); @@ -4739,8 +4747,7 @@ struct workqueue_struct *alloc_workqueue(const char *fmt, mutex_lock(&wq_pool_mutex);
mutex_lock(&wq->mutex); - for_each_pwq(pwq, wq) - pwq_adjust_max_active(pwq); + wq_adjust_max_active(wq); mutex_unlock(&wq->mutex);
list_add_tail_rcu(&wq->list, &workqueues); @@ -4878,8 +4885,6 @@ EXPORT_SYMBOL_GPL(destroy_workqueue); */ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active) { - struct pool_workqueue *pwq; - /* disallow meddling with max_active for ordered workqueues */ if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT)) return; @@ -4890,9 +4895,7 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
wq->flags &= ~__WQ_ORDERED; wq->saved_max_active = max_active; - - for_each_pwq(pwq, wq) - pwq_adjust_max_active(pwq); + wq_adjust_max_active(wq);
mutex_unlock(&wq->mutex); } @@ -5139,8 +5142,8 @@ static void show_pwq(struct pool_workqueue *pwq) pr_info(" pwq %d:", pool->id); pr_cont_pool_info(pool);
- pr_cont(" active=%d/%d refcnt=%d%s\n", - pwq->nr_active, pwq->max_active, pwq->refcnt, + pr_cont(" active=%d refcnt=%d%s\n", + pwq->nr_active, pwq->refcnt, !list_empty(&pwq->mayday_node) ? " MAYDAY" : "");
hash_for_each(pool->busy_hash, bkt, worker, hentry) { @@ -5688,7 +5691,6 @@ EXPORT_SYMBOL_GPL(work_on_cpu_safe_key); void freeze_workqueues_begin(void) { struct workqueue_struct *wq; - struct pool_workqueue *pwq;
mutex_lock(&wq_pool_mutex);
@@ -5697,8 +5699,7 @@ void freeze_workqueues_begin(void)
list_for_each_entry(wq, &workqueues, list) { mutex_lock(&wq->mutex); - for_each_pwq(pwq, wq) - pwq_adjust_max_active(pwq); + wq_adjust_max_active(wq); mutex_unlock(&wq->mutex); }
@@ -5763,7 +5764,6 @@ bool freeze_workqueues_busy(void) void thaw_workqueues(void) { struct workqueue_struct *wq; - struct pool_workqueue *pwq;
mutex_lock(&wq_pool_mutex);
@@ -5775,8 +5775,7 @@ void thaw_workqueues(void) /* restore max_active and repopulate worklist */ list_for_each_entry(wq, &workqueues, list) { mutex_lock(&wq->mutex); - for_each_pwq(pwq, wq) - pwq_adjust_max_active(pwq); + wq_adjust_max_active(wq); mutex_unlock(&wq->mutex); }