[PATCH 21/31] workqueue: drop WQ_RESCUER and test workqueue->rescuer for NULL instead

Tejun Heo
2013-03-02T03:28:59Z

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>
---
include/linux/workqueue.h | 1 -
kernel/workqueue.c | 22 ++++++++++------------
2 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 2683e8e..0341403 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -294,7 +294,6 @@ 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 1695bd6..bcc02bb 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1825,7 +1825,7 @@ 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 */
@@ -2283,7 +2283,7 @@ 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
@@ -2767,7 +2767,7 @@ 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);
@@ -3405,13 +3405,6 @@ 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);

@@ -3442,7 +3435,11 @@ 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();
@@ -3526,9 +3523,10 @@ 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;
}

/*
--
1.8.1.2