workqueue: add wokrqueue_struct->maydays list to replace mayday cpu iterators

Similar to how pool_workqueue iteration used to be, raising and
servicing mayday requests is based on CPU numbers.  It's hairy because
cpumask_t may not be able to handle WORK_CPU_UNBOUND and cpumasks are
assumed to be always set on UP.  This is ugly and can't handle
multiple unbound pools to be added for unbound workqueues w/ custom
attributes.

Add workqueue_struct->maydays.  When a pool_workqueue needs rescuing,
it gets chained on the list through pool_workqueue->mayday_node and
rescuer_thread() consumes the list until it's empty.

This patch doesn't introduce any visible behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 8942cc7..26c67c7 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -170,6 +170,7 @@ struct pool_workqueue {
        int                     max_active;     /* L: max active works */
        struct list_head        delayed_works;  /* L: delayed works */
        struct list_head        pwqs_node;      /* I: node on wq->pwqs */
+       struct list_head        mayday_node;    /* W: node on wq->maydays */
 } __aligned(1 << WORK_STRUCT_FLAG_BITS);
 
 /*
@@ -182,27 +183,6 @@ struct wq_flusher {
 };
 
 /*
- * All cpumasks are assumed to be always set on UP and thus can't be
- * used to determine whether there's something to be done.
- */
-#ifdef CONFIG_SMP
-typedef cpumask_var_t mayday_mask_t;
-#define mayday_test_and_set_cpu(cpu, mask)     \
-       cpumask_test_and_set_cpu((cpu), (mask))
-#define mayday_clear_cpu(cpu, mask)            cpumask_clear_cpu((cpu), (mask))
-#define for_each_mayday_cpu(cpu, mask)         for_each_cpu((cpu), (mask))
-#define alloc_mayday_mask(maskp, gfp)          zalloc_cpumask_var((maskp), (gfp))
-#define free_mayday_mask(mask)                 free_cpumask_var((mask))
-#else
-typedef unsigned long mayday_mask_t;
-#define mayday_test_and_set_cpu(cpu, mask)     test_and_set_bit(0, &(mask))
-#define mayday_clear_cpu(cpu, mask)            clear_bit(0, &(mask))
-#define for_each_mayday_cpu(cpu, mask)         if ((cpu) = 0, (mask))
-#define alloc_mayday_mask(maskp, gfp)          true
-#define free_mayday_mask(mask)                 do { } while (0)
-#endif
-
-/*
  * The externally visible workqueue abstraction is an array of
  * per-CPU workqueues:
  */
@@ -224,7 +204,7 @@ struct workqueue_struct {
        struct list_head        flusher_queue;  /* F: flush waiters */
        struct list_head        flusher_overflow; /* F: flush overflow list */
 
-       mayday_mask_t           mayday_mask;    /* cpus requesting rescue */
+       struct list_head        maydays;        /* W: pwqs requesting rescue */
        struct worker           *rescuer;       /* I: rescue worker */
 
        int                     nr_drainers;    /* W: drain in progress */
@@ -1850,23 +1830,21 @@ static void idle_worker_timeout(unsigned long __pool)
        spin_unlock_irq(&pool->lock);
 }
 
-static bool send_mayday(struct work_struct *work)
+static void send_mayday(struct work_struct *work)
 {
        struct pool_workqueue *pwq = get_work_pwq(work);
        struct workqueue_struct *wq = pwq->wq;
-       unsigned int cpu;
+
+       lockdep_assert_held(&workqueue_lock);
 
        if (!(wq->flags & WQ_RESCUER))
-               return false;
+               return;
 
        /* mayday mayday mayday */
-       cpu = pwq->pool->cpu;
-       /* WORK_CPU_UNBOUND can't be set in cpumask, use cpu 0 instead */
-       if (cpu == WORK_CPU_UNBOUND)
-               cpu = 0;
-       if (!mayday_test_and_set_cpu(cpu, wq->mayday_mask))
+       if (list_empty(&pwq->mayday_node)) {
+               list_add_tail(&pwq->mayday_node, &wq->maydays);
                wake_up_process(wq->rescuer->task);
-       return true;
+       }
 }
 
 static void pool_mayday_timeout(unsigned long __pool)
@@ -1874,7 +1852,8 @@ static void pool_mayday_timeout(unsigned long __pool)
        struct worker_pool *pool = (void *)__pool;
        struct work_struct *work;
 
-       spin_lock_irq(&pool->lock);
+       spin_lock_irq(&workqueue_lock);         /* for wq->maydays */
+       spin_lock(&pool->lock);
 
        if (need_to_create_worker(pool)) {
                /*
@@ -1887,7 +1866,8 @@ static void pool_mayday_timeout(unsigned long __pool)
                        send_mayday(work);
        }
 
-       spin_unlock_irq(&pool->lock);
+       spin_unlock(&pool->lock);
+       spin_unlock_irq(&workqueue_lock);
 
        mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);
 }
@@ -2336,8 +2316,6 @@ static int rescuer_thread(void *__rescuer)
        struct worker *rescuer = __rescuer;
        struct workqueue_struct *wq = rescuer->rescue_wq;
        struct list_head *scheduled = &rescuer->scheduled;
-       bool is_unbound = wq->flags & WQ_UNBOUND;
-       unsigned int cpu;
 
        set_user_nice(current, RESCUER_NICE_LEVEL);
 
@@ -2355,18 +2333,19 @@ repeat:
                return 0;
        }
 
-       /*
-        * See whether any cpu is asking for help.  Unbounded
-        * workqueues use cpu 0 in mayday_mask for CPU_UNBOUND.
-        */
-       for_each_mayday_cpu(cpu, wq->mayday_mask) {
-               unsigned int tcpu = is_unbound ? WORK_CPU_UNBOUND : cpu;
-               struct pool_workqueue *pwq = get_pwq(tcpu, wq);
+       /* see whether any pwq is asking for help */
+       spin_lock_irq(&workqueue_lock);
+
+       while (!list_empty(&wq->maydays)) {
+               struct pool_workqueue *pwq = list_first_entry(&wq->maydays,
+                                       struct pool_workqueue, mayday_node);
                struct worker_pool *pool = pwq->pool;
                struct work_struct *work, *n;
 
                __set_current_state(TASK_RUNNING);
-               mayday_clear_cpu(cpu, wq->mayday_mask);
+               list_del_init(&pwq->mayday_node);
+
+               spin_unlock_irq(&workqueue_lock);
 
                /* migrate to the target cpu if possible */
                worker_maybe_bind_and_lock(pool);
@@ -2392,9 +2371,12 @@ repeat:
                        wake_up_worker(pool);
 
                rescuer->pool = NULL;
-               spin_unlock_irq(&pool->lock);
+               spin_unlock(&pool->lock);
+               spin_lock(&workqueue_lock);
        }
 
+       spin_unlock_irq(&workqueue_lock);
+
        /* rescuers should never participate in concurrency management */
        WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
        schedule();
@@ -3192,6 +3174,7 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
        INIT_LIST_HEAD(&wq->pwqs);
        INIT_LIST_HEAD(&wq->flusher_queue);
        INIT_LIST_HEAD(&wq->flusher_overflow);
+       INIT_LIST_HEAD(&wq->maydays);
 
        lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
        INIT_LIST_HEAD(&wq->list);
@@ -3205,14 +3188,12 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
                pwq->flush_color = -1;
                pwq->max_active = max_active;
                INIT_LIST_HEAD(&pwq->delayed_works);
+               INIT_LIST_HEAD(&pwq->mayday_node);
        }
 
        if (flags & WQ_RESCUER) {
                struct worker *rescuer;
 
-               if (!alloc_mayday_mask(&wq->mayday_mask, GFP_KERNEL))
-                       goto err;
-
                wq->rescuer = rescuer = alloc_worker();
                if (!rescuer)
                        goto err;
@@ -3246,7 +3227,6 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
 err:
        if (wq) {
                free_pwqs(wq);
-               free_mayday_mask(wq->mayday_mask);
                kfree(wq->rescuer);
                kfree(wq);
        }
@@ -3289,7 +3269,6 @@ void destroy_workqueue(struct workqueue_struct *wq)
 
        if (wq->flags & WQ_RESCUER) {
                kthread_stop(wq->rescuer->task);
-               free_mayday_mask(wq->mayday_mask);
                kfree(wq->rescuer);
        }