workqueue: set PF_WQ_WORKER on rescuers
PF_WQ_WORKER is used to tell scheduler that the task is a workqueue
worker and needs wq_worker_sleeping/waking_up() invoked on it for
concurrency management. As rescuers never participate in concurrency
management, PF_WQ_WORKER wasn't set on them.
There's a need for an interface which can query whether %current is
executing a work item and if so which. Such interface requires a way
to identify all tasks which may execute work items and PF_WQ_WORKER
will be used for that. As all normal workers always have PF_WQ_WORKER
set, we only need to add it to rescuers.
As rescuers start with WORKER_PREP but never clear it, it's always
NOT_RUNNING and there's no need to worry about it interfering with
concurrency management even if PF_WQ_WORKER is set; however, unlike
normal workers, rescuers currently don't have its worker struct as
kthread_data(). It uses the associated workqueue_struct instead.
This is problematic as wq_worker_sleeping/waking_up() expect struct
worker at kthread_data().
This patch adds worker->rescue_wq and start rescuer kthreads with
worker struct as kthread_data and sets PF_WQ_WORKER on rescuers.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 7967f34..6b99ac7 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -149,6 +149,9 @@
/* for rebinding worker to CPU */
struct work_struct rebind_work; /* L: for busy worker */
+
+ /* used only by rescuers to point to the target workqueue */
+ struct workqueue_struct *rescue_wq; /* I: the workqueue to rescue */
};
struct worker_pool {
@@ -763,12 +766,20 @@
unsigned int cpu)
{
struct worker *worker = kthread_data(task), *to_wakeup = NULL;
- struct worker_pool *pool = worker->pool;
- atomic_t *nr_running = get_pool_nr_running(pool);
+ struct worker_pool *pool;
+ atomic_t *nr_running;
+ /*
+ * Rescuers, which may not have all the fields set up like normal
+ * workers, also reach here, let's not access anything before
+ * checking NOT_RUNNING.
+ */
if (worker->flags & WORKER_NOT_RUNNING)
return NULL;
+ pool = worker->pool;
+ nr_running = get_pool_nr_running(pool);
+
/* this can only happen on the local cpu */
BUG_ON(cpu != raw_smp_processor_id());
@@ -2357,7 +2368,7 @@
/**
* rescuer_thread - the rescuer thread function
- * @__wq: the associated workqueue
+ * @__rescuer: self
*
* Workqueue rescuer thread function. There's one rescuer for each
* workqueue which has WQ_RESCUER set.
@@ -2374,20 +2385,27 @@
*
* This should happen rarely.
*/
-static int rescuer_thread(void *__wq)
+static int rescuer_thread(void *__rescuer)
{
- struct workqueue_struct *wq = __wq;
- struct worker *rescuer = wq->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);
+
+ /*
+ * Mark rescuer as worker too. As WORKER_PREP is never cleared, it
+ * doesn't participate in concurrency management.
+ */
+ rescuer->task->flags |= PF_WQ_WORKER;
repeat:
set_current_state(TASK_INTERRUPTIBLE);
if (kthread_should_stop()) {
__set_current_state(TASK_RUNNING);
+ rescuer->task->flags &= ~PF_WQ_WORKER;
return 0;
}
@@ -2431,6 +2449,8 @@
spin_unlock_irq(&gcwq->lock);
}
+ /* rescuers should never participate in concurrency management */
+ WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
schedule();
goto repeat;
}
@@ -3266,7 +3286,8 @@
if (!rescuer)
goto err;
- rescuer->task = kthread_create(rescuer_thread, wq, "%s",
+ rescuer->rescue_wq = wq;
+ rescuer->task = kthread_create(rescuer_thread, rescuer, "%s",
wq->name);
if (IS_ERR(rescuer->task))
goto err;