workqueue: drop WQ_RESCUER and test workqueue->rescuer for NULL instead

WQ_RESCUER is superflous.  WQ_MEM_RECLAIM indicates that the user
wants a rescuer and testing wq->rescuer for NULL can answer whether a
given workqueue has a rescuer or not.  Drop WQ_RESCUER and test
wq->rescuer directly.

This will help simplifying __alloc_workqueue_key() failure path by
allowing it to use destroy_workqueue() on a partially constructed
workqueue, which in turn will help implementing dynamic management of
pool_workqueues.

While at it, clear wq->rescuer after freeing it in
destroy_workqueue().  This is a precaution as scheduled changes will
make destruction more complex.

This patch doesn't introduce any functional changes.

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

2 files changed, 10 insertions, 13 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 00c1b9ba8252..c270b4eedf16 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -295,7 +295,6 @@ enum {
         WQ_CPU_INTENSIVE        = 1 << 5, /* cpu instensive workqueue */
 
         WQ_DRAINING             = 1 << 6, /* internal: workqueue is draining */
-        WQ_RESCUER              = 1 << 7, /* internal: workqueue has rescuer */
 
         WQ_MAX_ACTIVE           = 512,    /* I like 512, better ideas? */
         WQ_MAX_UNBOUND_PER_CPU  = 4,      /* 4 * #cpus for unbound wq */
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a8b86f7b6e34..7ff2b9c5cc3a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1827,7 +1827,7 @@ static void send_mayday(struct work_struct *work)
 
         lockdep_assert_held(&workqueue_lock);
 
-        if (!(wq->flags & WQ_RESCUER))
+        if (!wq->rescuer)
                 return;
 
         /* mayday mayday mayday */
@@ -2285,7 +2285,7 @@ sleep:
  * @__rescuer: self
  *
  * Workqueue rescuer thread function.  There's one rescuer for each
- * workqueue which has WQ_RESCUER set.
+ * workqueue which has WQ_MEM_RECLAIM set.
  *
  * Regular work processing on a pool may block trying to create a new
  * worker which uses GFP_KERNEL allocation which has slight chance of
@@ -2769,7 +2769,7 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr)
          * flusher is not running on the same workqueue by verifying write
          * access.
          */
-        if (pwq->wq->saved_max_active == 1 || pwq->wq->flags & WQ_RESCUER)
+        if (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer)
                 lock_map_acquire(&pwq->wq->lockdep_map);
         else
                 lock_map_acquire_read(&pwq->wq->lockdep_map);
@@ -3412,13 +3412,6 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
         va_end(args);
         va_end(args1);
 
-        /*
-         * Workqueues which may be used during memory reclaim should
-         * have a rescuer to guarantee forward progress.
-         */
-        if (flags & WQ_MEM_RECLAIM)
-                flags |= WQ_RESCUER;
-
         max_active = max_active ?: WQ_DFL_ACTIVE;
         max_active = wq_clamp_max_active(max_active, flags, wq->name);
 
@@ -3449,7 +3442,11 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
         }
         local_irq_enable();
 
-        if (flags & WQ_RESCUER) {
+        /*
+         * Workqueues which may be used during memory reclaim should
+         * have a rescuer to guarantee forward progress.
+         */
+        if (flags & WQ_MEM_RECLAIM) {
                 struct worker *rescuer;
 
                 wq->rescuer = rescuer = alloc_worker();
@@ -3533,9 +3530,10 @@ void destroy_workqueue(struct workqueue_struct *wq)
 
         spin_unlock_irq(&workqueue_lock);
 
-        if (wq->flags & WQ_RESCUER) {
+        if (wq->rescuer) {
                 kthread_stop(wq->rescuer->task);
                 kfree(wq->rescuer);
+                wq->rescuer = NULL;
         }
 
         /*