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Subjectwork item still be scheduled to execute after destroy_workqueue?
Hi Lai and Tejun,

Why can the work still be queued to and executed when queueing it to a
wq has been destroyed, for instance, the below code snippet in a
kernel module:
---------------------->8---------------------

struct workqueue_struct *wq0;
#define MAX_ACTIVE_WORKS (3)

static void work0_func(struct work_struct *work);
static void work1_func(struct work_struct *work);
static void work2_func(struct work_struct *work);

static DECLARE_WORK(w0, work0_func);
static DECLARE_WORK(w1, work1_func);
static DECLARE_WORK(w2, work2_func);

/* work->func */
static void work0_func(struct work_struct *work)
{
pr_info("+%s begins to sleep\n", __func__);
/* sleep for 10s */
schedule_timeout_interruptible(msecs_to_jiffies(10000));
pr_info("+%s after sleep, begin to queue another work\n", __func__);
queue_work_on(1, wq0, &w1);
}

/* work->func */
static void work1_func(struct work_struct *work)
{
pr_info("+%s scheduled\n", __func__);
}

/* work->func */
static void work2_func(struct work_struct *work)
{
pr_info("+%s scheduled\n", __func__);
}

static int destroy_init(void)
{
wq0 = alloc_workqueue("percpu_wq0", 0, MAX_ACTIVE_WORKS);
if (!wq0) {
pr_err("alloc_workqueue failed\n");
return -1;
}
queue_work_on(1, wq0, &w0);
pr_info("Begin to destroy wq0...\n");
destroy_workqueue(wq0);
pr_info("queue w2 to the wq0 after destroyed...\n");
queue_work_on(1, wq0, &w2);

return 0;
}

The output on my x86_64 box is:

[344702.734480] +destroy_init+
[344702.734499] Begin to destroy wq0...
[344702.734516] +work0_func begins to sleep
[344712.791607] +work0_func after sleep, begin to queue another work
[344712.791620] +work1_func scheduled
[344712.791649] queue w2 to the wq0 after destroyed...
[344712.791663] +work2_func scheduled <------------- work 2 still be scheduled?

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