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simplify cleanup_workqueue_thread()

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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>
This commit is contained in:
Oleg Nesterov 2007-05-23 13:57:57 -07:00 committed by Linus Torvalds
parent 3fcbc72965
commit 14441960e8
1 changed files with 37 additions and 47 deletions
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84
kernel/workqueue.c
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@ -47,7 +47,6 @@ struct cpu_workqueue_struct {
struct workqueue_struct *wq;
struct task_struct *thread;
int should_stop;
int run_depth; /* Detect run_workqueue() recursion depth */
} ____cacheline_aligned;
@ -71,7 +70,13 @@ static LIST_HEAD(workqueues);
static int singlethread_cpu __read_mostly;
static cpumask_t cpu_singlethread_map __read_mostly;
/* optimization, we could use cpu_possible_map */
/*
* _cpu_down() first removes CPU from cpu_online_map, then CPU_DEAD
* flushes cwq->worklist. This means that flush_workqueue/wait_on_work
* which comes in between can't use for_each_online_cpu(). We could
* use cpu_possible_map, the cpumask below is more a documentation
* than optimization.
*/
static cpumask_t cpu_populated_map __read_mostly;
/* If it's single threaded, it isn't in the list of workqueues. */
@ -272,24 +277,6 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
spin_unlock_irq(&cwq->lock);
}
/*
* NOTE: the caller must not touch *cwq if this func returns true
*/
static int cwq_should_stop(struct cpu_workqueue_struct *cwq)
{
int should_stop = cwq->should_stop;
if (unlikely(should_stop)) {
spin_lock_irq(&cwq->lock);
should_stop = cwq->should_stop && list_empty(&cwq->worklist);
if (should_stop)
cwq->thread = NULL;
spin_unlock_irq(&cwq->lock);
}
return should_stop;
}
static int worker_thread(void *__cwq)
{
struct cpu_workqueue_struct *cwq = __cwq;
@ -302,14 +289,15 @@ static int worker_thread(void *__cwq)
for (;;) {
prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
if (!freezing(current) && !cwq->should_stop
&& list_empty(&cwq->worklist))
if (!freezing(current) &&
!kthread_should_stop() &&
list_empty(&cwq->worklist))
schedule();
finish_wait(&cwq->more_work, &wait);
try_to_freeze();
if (cwq_should_stop(cwq))
if (kthread_should_stop())
break;
run_workqueue(cwq);
@ -340,18 +328,21 @@ static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
insert_work(cwq, &barr->work, tail);
}
static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
{
int active;
if (cwq->thread == current) {
/*
* Probably keventd trying to flush its own queue. So simply run
* it by hand rather than deadlocking.
*/
run_workqueue(cwq);
active = 1;
} else {
struct wq_barrier barr;
int active = 0;
active = 0;
spin_lock_irq(&cwq->lock);
if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
insert_wq_barrier(cwq, &barr, 1);
@ -362,6 +353,8 @@ static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
if (active)
wait_for_completion(&barr.done);
}
return active;
}
/**
@ -674,7 +667,6 @@ static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
return PTR_ERR(p);
cwq->thread = p;
cwq->should_stop = 0;
return 0;
}
@ -740,29 +732,27 @@ EXPORT_SYMBOL_GPL(__create_workqueue);
static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
{
struct wq_barrier barr;
int alive = 0;
/*
* Our caller is either destroy_workqueue() or CPU_DEAD,
* workqueue_mutex protects cwq->thread
*/
if (cwq->thread == NULL)
return;
spin_lock_irq(&cwq->lock);
if (cwq->thread != NULL) {
insert_wq_barrier(cwq, &barr, 1);
cwq->should_stop = 1;
alive = 1;
}
spin_unlock_irq(&cwq->lock);
/*
* If the caller is CPU_DEAD the single flush_cpu_workqueue()
* is not enough, a concurrent flush_workqueue() can insert a
* barrier after us.
* When ->worklist becomes empty it is safe to exit because no
* more work_structs can be queued on this cwq: flush_workqueue
* checks list_empty(), and a "normal" queue_work() can't use
* a dead CPU.
*/
while (flush_cpu_workqueue(cwq))
;
if (alive) {
wait_for_completion(&barr.done);
while (unlikely(cwq->thread != NULL))
cpu_relax();
/*
* Wait until cwq->thread unlocks cwq->lock,
* it won't touch *cwq after that.
*/
smp_rmb();
spin_unlock_wait(&cwq->lock);
}
kthread_stop(cwq->thread);
cwq->thread = NULL;
}
/**