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SUNRPC: Fix a livelock problem in the xprt->backlog queue

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This patch ensures that we throttle new RPC requests if there are
requests already waiting in the xprt->backlog queue. The reason for
doing this is to fix livelock issues that can occur when an existing
(high priority) task is waiting in the backlog queue, gets woken up
by xprt_free_slot(), but a new task then steals the slot.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
This commit is contained in:
Trond Myklebust
2013-04-14 10:49:37 -04:00
parent b570a975ed
commit ba60eb25ff
3 changed files with 76 additions and 4 deletions
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17
net/sunrpc/clnt.c
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@@ -1306,6 +1306,8 @@ call_reserve(struct rpc_task *task)
xprt_reserve(task);
}
static void call_retry_reserve(struct rpc_task *task);
/*
* 1b. Grok the result of xprt_reserve()
*/
@@ -1347,7 +1349,7 @@ call_reserveresult(struct rpc_task *task)
case -ENOMEM:
rpc_delay(task, HZ >> 2);
case -EAGAIN: /* woken up; retry */
task->tk_action = call_reserve;
task->tk_action = call_retry_reserve;
return;
case -EIO: /* probably a shutdown */
break;
@@ -1359,6 +1361,19 @@ call_reserveresult(struct rpc_task *task)
rpc_exit(task, status);
}
/*
* 1c. Retry reserving an RPC call slot
*/
static void
call_retry_reserve(struct rpc_task *task)
{
dprint_status(task);
task->tk_status = 0;
task->tk_action = call_reserveresult;
xprt_retry_reserve(task);
}
/*
* 2. Bind and/or refresh the credentials
*/