On Thu, 7 Dec 2006 10:51:48 -0800
Andrew Morton <[email protected]> wrote:
> + if (!cpu_online(cpu)) /* oops, CPU got unplugged */
> + goto bail;
hm, actually we can pull the same trick with flush_scheduled_work().
Should fix quite a few things...
From: Andrew Morton <[email protected]>
We have a class of deadlocks where the flush_scheduled_work() caller can get
stuck waiting for a work to complete, where that work wants to take
workqueue_mutex for some reason.
Fix this by not holding workqueue_mutex when waiting for a workqueue to flush.
The patch assumes that the per-cpu workqueue won't get freed up while there's
a task waiting on cpu_workqueue_struct.work_done. If that can happen,
run_workqueue() would crash anyway.
Cc: Bjorn Helgaas <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Srivatsa Vaddagiri <[email protected]>
Cc: Gautham shenoy <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
kernel/workqueue.c | 22 +++++++++++++++++++---
1 files changed, 19 insertions(+), 3 deletions(-)
diff -puN kernel/workqueue.c~workqueue-dont-hold-workqueue_mutex-in-flush_scheduled_work kernel/workqueue.c
--- a/kernel/workqueue.c~workqueue-dont-hold-workqueue_mutex-in-flush_scheduled_work
+++ a/kernel/workqueue.c
@@ -325,14 +325,22 @@ static int worker_thread(void *__cwq)
return 0;
}
-static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
+/*
+ * If cpu == -1 it's a single-threaded workqueue and the caller does not hold
+ * workqueue_mutex
+ */
+static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq, int cpu)
{
if (cwq->thread == current) {
/*
* Probably keventd trying to flush its own queue. So simply run
* it by hand rather than deadlocking.
*/
+ if (cpu != -1)
+ mutex_unlock(&workqueue_mutex);
run_workqueue(cwq);
+ if (cpu != -1)
+ mutex_lock(&workqueue_mutex);
} else {
DEFINE_WAIT(wait);
long sequence_needed;
@@ -344,7 +352,14 @@ static void flush_cpu_workqueue(struct c
prepare_to_wait(&cwq->work_done, &wait,
TASK_UNINTERRUPTIBLE);
spin_unlock_irq(&cwq->lock);
+ if (cpu != -1)
+ mutex_unlock(&workqueue_mutex);
schedule();
+ if (cpu != -1) {
+ mutex_lock(&workqueue_mutex);
+ if (!cpu_online(cpu))
+ return; /* oops, CPU unplugged */
+ }
spin_lock_irq(&cwq->lock);
}
finish_wait(&cwq->work_done, &wait);
@@ -373,13 +388,14 @@ void fastcall flush_workqueue(struct wor
if (is_single_threaded(wq)) {
/* Always use first cpu's area. */
- flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu));
+ flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu),
+ -1);
} else {
int cpu;
mutex_lock(&workqueue_mutex);
for_each_online_cpu(cpu)
- flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
+ flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu), cpu);
mutex_unlock(&workqueue_mutex);
}
}
_
-
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