workqueue: avoid recursion in run_workqueue()
1) lockdep will complain when run_workqueue() performs recursion.
2) The recursive implementation of run_workqueue() means that
flush_workqueue() and its documentation are inconsistent. This may
hide deadlocks and other bugs.
3) The recursion in run_workqueue() will poison cwq->current_work, but
flush_work() and __cancel_work_timer(), etcetera need a reliable
cwq->current_work.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Eric Dumazet <dada1@cosmosbay.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9aedd9f..32f8e0d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -48,8 +48,6 @@
struct workqueue_struct *wq;
struct task_struct *thread;
-
- int run_depth; /* Detect run_workqueue() recursion depth */
} ____cacheline_aligned;
/*
@@ -262,13 +260,6 @@
static void run_workqueue(struct cpu_workqueue_struct *cwq)
{
spin_lock_irq(&cwq->lock);
- cwq->run_depth++;
- if (cwq->run_depth > 3) {
- /* morton gets to eat his hat */
- printk("%s: recursion depth exceeded: %d\n",
- __func__, cwq->run_depth);
- dump_stack();
- }
while (!list_empty(&cwq->worklist)) {
struct work_struct *work = list_entry(cwq->worklist.next,
struct work_struct, entry);
@@ -311,7 +302,6 @@
spin_lock_irq(&cwq->lock);
cwq->current_work = NULL;
}
- cwq->run_depth--;
spin_unlock_irq(&cwq->lock);
}
@@ -368,29 +358,20 @@
static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
{
- int active;
+ int active = 0;
+ struct wq_barrier barr;
- if (cwq->thread == current) {
- /*
- * Probably keventd trying to flush its own queue. So simply run
- * it by hand rather than deadlocking.
- */
- run_workqueue(cwq);
+ WARN_ON(cwq->thread == current);
+
+ spin_lock_irq(&cwq->lock);
+ if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
+ insert_wq_barrier(cwq, &barr, &cwq->worklist);
active = 1;
- } else {
- struct wq_barrier barr;
-
- active = 0;
- spin_lock_irq(&cwq->lock);
- if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
- insert_wq_barrier(cwq, &barr, &cwq->worklist);
- active = 1;
- }
- spin_unlock_irq(&cwq->lock);
-
- if (active)
- wait_for_completion(&barr.done);
}
+ spin_unlock_irq(&cwq->lock);
+
+ if (active)
+ wait_for_completion(&barr.done);
return active;
}