[PATCH v2] core: workqueue: return on workqueue recursion

From: Simon Kagstrom
Date: Thu Feb 04 2010 - 03:02:29 EST


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@xxxxxxxxxxxxxx>
---
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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