Before the rescuer is picked to running, the works of the @pwq
may be processed by some other workers, and destroy_workqueue()
may called at the same time. This may result a nasty situation
that rescuer may exit with non-empty mayday list.
It is no harm currently, destroy_workqueue() can safely to free
them all(workqueue&pwqs) togerther, since the rescuer is stopped.
No rescuer nor mayday-timer can access the mayday list.
But it is nasty and error-prone in future development. Fix it.
Signed-off-by: Lai Jiangshan <la...@cn.fujitsu.com>
---
kernel/workqueue.c | 21 +++++++++++++++------
1 files changed, 15 insertions(+), 6 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0ee63af..7539244 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2398,6 +2398,7 @@ static int rescuer_thread(void *__rescuer)
struct worker *rescuer = __rescuer;
struct workqueue_struct *wq = rescuer->rescue_wq;
struct list_head *scheduled = &rescuer->scheduled;
+ bool should_stop;
set_user_nice(current, RESCUER_NICE_LEVEL);
@@ -2408,12 +2409,14 @@ static int rescuer_thread(void *__rescuer)
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;
- }
+ /*
+ * When the rescuer is requested to stop, the workqueue has no
+ * work pending, but wq->maydays may still have pwq(s) queued.
+ * This can happend when some other workers process all works
+ * before this rescuer is scheduled. The rescuer must process
+ * all pwq(s) before exit.
+ */
+ should_stop = kthread_should_stop();
/* see whether any pwq is asking for help */
spin_lock_irq(&wq_mayday_lock);
@@ -2459,6 +2462,12 @@ repeat:
spin_unlock_irq(&wq_mayday_lock);
+ if (should_stop) {
+ __set_current_state(TASK_RUNNING);
+ rescuer->task->flags &= ~PF_WQ_WORKER;
+ return 0;
+ }
+
/* rescuers should never participate in concurrency management */
WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
schedule();
--
1.7.4.4
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