lkml.org 
[lkml]   [2006]   [Dec]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: workqueue deadlock
On Thu, 7 Dec 2006 10:51:48 -0800
Andrew Morton <akpm@osdl.org> 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 <akpm@osdl.org>

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 <bjorn.helgaas@hp.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: Gautham shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

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);
}
}
_
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-12-07 20:41    [W:0.088 / U:2.460 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site