flush_workqueue(): use preempt_disable to hold off cpu hotplug

Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: Gautham Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 6 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 918d55267a12..5176d51bcc2a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -419,18 +419,22 @@ static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
                  * Probably keventd trying to flush its own queue. So simply run
                  * it by hand rather than deadlocking.
                  */
-                mutex_unlock(&workqueue_mutex);
+                preempt_enable();
+                /*
+                 * We can still touch *cwq here because we are keventd, and
+                 * hot-unplug will be waiting us to exit.
+                 */
                 run_workqueue(cwq);
-                mutex_lock(&workqueue_mutex);
+                preempt_disable();
         } else {
                 struct wq_barrier barr;
 
                 init_wq_barrier(&barr);
                 __queue_work(cwq, &barr.work);
 
-                mutex_unlock(&workqueue_mutex);
+                preempt_enable();       /* Can no longer touch *cwq */
                 wait_for_completion(&barr.done);
-                mutex_lock(&workqueue_mutex);
+                preempt_disable();
         }
 }
 
@@ -449,7 +453,7 @@ static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
  */
 void fastcall flush_workqueue(struct workqueue_struct *wq)
 {
-        mutex_lock(&workqueue_mutex);
+        preempt_disable();              /* CPU hotplug */
         if (is_single_threaded(wq)) {
                 /* Always use first cpu's area. */
                 flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu));
@@ -459,7 +463,7 @@ void fastcall flush_workqueue(struct workqueue_struct *wq)
                 for_each_online_cpu(cpu)
                         flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
         }
-        mutex_unlock(&workqueue_mutex);
+        preempt_enable();
 }
 EXPORT_SYMBOL_GPL(flush_workqueue);