Messages in this thread | | | Date | Thu, 22 Jan 2009 10:36:49 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 2/3] workqueue: not allow recursion run_workqueue |
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* Frederic Weisbecker <fweisbec@gmail.com> wrote:
> On Thu, Jan 22, 2009 at 05:14:24PM +0800, Lai Jiangshan wrote: > > 1) lockdep will complain when recursion run_workqueue > > 2) works is not run orderly when recursion run_workqueue > > > > 3) BUG! > > We use recursion run_workqueue to hidden deadlock when > > keventd trying to flush its own queue. > > > > It's bug. When flush_workqueue()(nested in a work callback)returns, > > the workqueue is not really flushed, the sequence statement of > > this work callback will do some thing bad. > > > > So we should not allow workqueue trying to flush its own queue. > > > > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> > > --- > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > > index 2f44583..1129cde 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); > > - active = 1; > > - } else { > > - struct wq_barrier barr; > > + BUG_ON(cwq->thread == current); > > Hi Lai, > > BUG_ON seems perhaps a bit too much for such case. The system > will run in an endless loop because of a mistake that will not have > necessarily a fatal end. > WARN_ON should be enough (plus the warn that lockdep will raise > too in this case).
WARN_ONCE() is the best method usually - we want a one-time and expressive warning, not just a stack dump. (i.e. not WARN_ON and not WARN_ON_ONCE)
Plus some thinking needs to be put into exiting from that function in a way that the system will still be usable enough to report the bug.
Ingo
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