linux-kernel - [PATCH v2] core: workqueue: return on workqueue recursion

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Date:	Thu, 4 Feb 2010 09:02:16 +0100
From:	Simon Kagstrom <simon.kagstrom@...insight.net>
To:	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	linux-kernel@...r.kernel.org
Cc:	laijs@...fujitsu.com, rusty@...tcorp.com.au,
	akpm@...ux-foundation.org, mingo@...e.hu
Subject: [PATCH v2] core: workqueue: return on workqueue recursion

When the workqueue is flushed from workqueue context (recursively), the
system enters a strange state where things at random (dependent on the
global workqueue) start misbehaving. For example, for us the console and
logins locks up while the web server continues running.

The system becomes unstable since the workqueue barrier locks the
workqueue. This patch instead returns if the workqueue is flushed
recursively, which keeps the workqueue alive but warns.

Signed-off-by: Simon Kagstrom <simon.kagstrom@...insight.net>
---
ChangeLog:
	* Instead of BUG_ON, warn and return on recursive calls as suggested
	  by Oleg Nesterov and Tejun Hao

 kernel/workqueue.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index dee4865..49f8fa7 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -482,7 +482,8 @@ static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
 	int active = 0;
 	struct wq_barrier barr;
 
-	WARN_ON(cwq->thread == current);
+	if (WARN_ON(cwq->thread == current))
+		return 1;
 
 	spin_lock_irq(&cwq->lock);
 	if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
-- 
1.6.0.4

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