Merge "workqueue: fix possible livelock with concurrent mod_delayed_work()"

kernel/workqueue.c

@@ -50,6 +50,8 @@
 #include <linux/uaccess.h>
 #include <linux/sched/isolation.h>
 #include <linux/nmi.h>
+#include <linux/bug.h>
+#include <linux/delay.h>
 
 #include "workqueue_internal.h"
 
@@ -1305,6 +1307,12 @@ fail:
 	if (work_is_canceling(work))
 		return -ENOENT;
 	cpu_relax();
+	/*
+	 * The queueing is in progress in another context. If we keep
+	 * taking the pool->lock in a busy loop, the other context may
+	 * never get the lock. Give 1 usec delay to avoid this contention.
+	 */
+	udelay(1);
 	return -EAGAIN;
 }