SUNRPC: When changing the queue priority, ensure that we change the owner

This fixes a livelock in the xprt->sending queue where we end up never making progress on lower priority tasks because sleep_on_priority() keeps adding new tasks with the same owner to the head of the queue, and priority bumps mean that we keep resetting the queue->owner to whatever task is at the head of the queue. Regression introduced by commit c05eecf636101dd4347b2d8fa457626bf0088e0a (SUNRPC: Don't allow low priority tasks to pre-empt higher priority ones).

Trond Myklebust committed 13 years ago

Commit edd2e361 parent ab225411 file · +17 −1Browse files

Unified · Split

net/sunrpc/sched.c+17−1

@@ -98,9 +98,25 @@ __rpc_add_timer(struct rpc_wait_queue queue, struct rpc_task task) · 97 unmodified lines
98	98	list_add(&task->u.tk_wait.timer_list, &queue->timer_list.list);
99	99	}
100	100
	101	+static void rpc_rotate_queue_owner(struct rpc_wait_queue *queue)
	102	+{
	103	+ struct list_head *q = &queue->tasks[queue->priority];
	104	+ struct rpc_task *task;
	105	+
	106	+ if (!list_empty(q)) {
	107	+ task = list_first_entry(q, struct rpc_task, u.tk_wait.list);
	108	+ if (task->tk_owner == queue->owner)
	109	+ list_move_tail(&task->u.tk_wait.list, q);
	110	+ }
	111	+}
	112	+
101	113	static void rpc_set_waitqueue_priority(struct rpc_wait_queue *queue, int priority)
102	114	{
103		− queue->priority = priority;
	115	+ if (queue->priority != priority) {
	116	+ /* Fairness: rotate the list when changing priority */
	117	+ rpc_rotate_queue_owner(queue);
	118	+ queue->priority = priority;
	119	+ }
104	120	}
105	121
106	122	static void rpc_set_waitqueue_owner(struct rpc_wait_queue *queue, pid_t pid)