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>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 918d55267a12a98c43aa1c9ee43e17644712af8d..5176d51bcc2a97bc0f84d6797f492f7aab0bcf8a 100644 (file)
--- 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);