From 2355b70fd59cb5be7de2052a9edeee7afb7ff099 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Thu, 2 Apr 2009 16:58:24 -0700 Subject: [PATCH] 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 Acked-by: Oleg Nesterov Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Frederic Weisbecker Cc: Eric Dumazet Cc: Rusty Russell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/workqueue.c | 41 +++++++++++------------------------------ 1 file changed, 11 insertions(+), 30 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 9aedd9fd825..32f8e0d2bf5 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -48,8 +48,6 @@ struct cpu_workqueue_struct { struct workqueue_struct *wq; struct task_struct *thread; - - int run_depth; /* Detect run_workqueue() recursion depth */ } ____cacheline_aligned; /* @@ -262,13 +260,6 @@ EXPORT_SYMBOL_GPL(queue_delayed_work_on); 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 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq) spin_lock_irq(&cwq->lock); cwq->current_work = NULL; } - cwq->run_depth--; spin_unlock_irq(&cwq->lock); } @@ -368,29 +358,20 @@ static void insert_wq_barrier(struct cpu_workqueue_struct *cwq, 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; }