simplify cleanup_workqueue_thread()
cleanup_workqueue_thread() and cwq_should_stop() are overcomplicated. Convert the code to use kthread_should_stop/kthread_stop as was suggested by Gautham and Srivatsa. In particular this patch removes the (unlikely) busy-wait loop from the exit path, it was a temporary and ugly kludge (if not a bug). Note: the current code was designed to solve another old problem: work->func can't share locks with hotplug callbacks. I think this could be done, see http://marc.info/?l=linux-kernel&m=116905366428633 but this needs some more complications to preserve CPU affinity of cwq->thread during cpu_up(). A freezer-based hotplug looks more appealing. [akpm@linux-foundation.org: make it more tolerant of gcc borkenness] Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: Zilvinas Valinskas <zilvinas@wilibox.com> Cc: Gautham R Shenoy <ego@in.ibm.com> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Cc: "Rafael J. Wysocki" <rjw@sisk.pl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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14441960e8
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@ -47,7 +47,6 @@ struct cpu_workqueue_struct {
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struct workqueue_struct *wq;
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struct task_struct *thread;
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int should_stop;
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int run_depth; /* Detect run_workqueue() recursion depth */
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} ____cacheline_aligned;
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@ -71,7 +70,13 @@ static LIST_HEAD(workqueues);
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static int singlethread_cpu __read_mostly;
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static cpumask_t cpu_singlethread_map __read_mostly;
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/* optimization, we could use cpu_possible_map */
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/*
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* _cpu_down() first removes CPU from cpu_online_map, then CPU_DEAD
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* flushes cwq->worklist. This means that flush_workqueue/wait_on_work
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* which comes in between can't use for_each_online_cpu(). We could
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* use cpu_possible_map, the cpumask below is more a documentation
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* than optimization.
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*/
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static cpumask_t cpu_populated_map __read_mostly;
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/* If it's single threaded, it isn't in the list of workqueues. */
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@ -272,24 +277,6 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
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spin_unlock_irq(&cwq->lock);
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}
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/*
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* NOTE: the caller must not touch *cwq if this func returns true
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*/
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static int cwq_should_stop(struct cpu_workqueue_struct *cwq)
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{
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int should_stop = cwq->should_stop;
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if (unlikely(should_stop)) {
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spin_lock_irq(&cwq->lock);
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should_stop = cwq->should_stop && list_empty(&cwq->worklist);
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if (should_stop)
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cwq->thread = NULL;
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spin_unlock_irq(&cwq->lock);
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}
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return should_stop;
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}
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static int worker_thread(void *__cwq)
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{
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struct cpu_workqueue_struct *cwq = __cwq;
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@ -302,14 +289,15 @@ static int worker_thread(void *__cwq)
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for (;;) {
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prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
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if (!freezing(current) && !cwq->should_stop
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&& list_empty(&cwq->worklist))
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if (!freezing(current) &&
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!kthread_should_stop() &&
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list_empty(&cwq->worklist))
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schedule();
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finish_wait(&cwq->more_work, &wait);
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try_to_freeze();
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if (cwq_should_stop(cwq))
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if (kthread_should_stop())
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break;
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run_workqueue(cwq);
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@ -340,18 +328,21 @@ static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
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insert_work(cwq, &barr->work, tail);
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}
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static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
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static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
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{
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int active;
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if (cwq->thread == current) {
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/*
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* Probably keventd trying to flush its own queue. So simply run
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* it by hand rather than deadlocking.
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*/
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run_workqueue(cwq);
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active = 1;
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} else {
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struct wq_barrier barr;
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int active = 0;
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active = 0;
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spin_lock_irq(&cwq->lock);
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if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
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insert_wq_barrier(cwq, &barr, 1);
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@ -362,6 +353,8 @@ static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
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if (active)
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wait_for_completion(&barr.done);
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}
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return active;
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}
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/**
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@ -674,7 +667,6 @@ static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
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return PTR_ERR(p);
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cwq->thread = p;
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cwq->should_stop = 0;
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return 0;
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}
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@ -740,29 +732,27 @@ EXPORT_SYMBOL_GPL(__create_workqueue);
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static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
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{
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struct wq_barrier barr;
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int alive = 0;
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/*
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* Our caller is either destroy_workqueue() or CPU_DEAD,
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* workqueue_mutex protects cwq->thread
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*/
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if (cwq->thread == NULL)
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return;
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spin_lock_irq(&cwq->lock);
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if (cwq->thread != NULL) {
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insert_wq_barrier(cwq, &barr, 1);
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cwq->should_stop = 1;
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alive = 1;
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}
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spin_unlock_irq(&cwq->lock);
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/*
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* If the caller is CPU_DEAD the single flush_cpu_workqueue()
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* is not enough, a concurrent flush_workqueue() can insert a
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* barrier after us.
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* When ->worklist becomes empty it is safe to exit because no
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* more work_structs can be queued on this cwq: flush_workqueue
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* checks list_empty(), and a "normal" queue_work() can't use
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* a dead CPU.
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*/
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while (flush_cpu_workqueue(cwq))
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;
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if (alive) {
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wait_for_completion(&barr.done);
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while (unlikely(cwq->thread != NULL))
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cpu_relax();
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/*
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* Wait until cwq->thread unlocks cwq->lock,
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* it won't touch *cwq after that.
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*/
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smp_rmb();
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spin_unlock_wait(&cwq->lock);
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}
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kthread_stop(cwq->thread);
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cwq->thread = NULL;
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}
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/**
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