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authorNeilBrown <neilb@suse.de>2021-05-17 09:59:10 +1000
committerTrond Myklebust <trond.myklebust@hammerspace.com>2021-05-20 12:17:08 -0400
commite877a88d1f069edced4160792f42c2a8e2dba942 (patch)
treeaa703cd2dc053859047e9d0feb9c98629ad4119e /net/sunrpc/clnt.c
parentd1d973950aceecd646ea3bee66764414bfeac072 (diff)
SUNRPC in case of backlog, hand free slots directly to waiting task
If sunrpc.tcp_max_slot_table_entries is small and there are tasks on the backlog queue, then when a request completes it is freed and the first task on the queue is woken. The expectation is that it will wake and claim that request. However if it was a sync task and the waiting process was killed at just that moment, it will wake and NOT claim the request. As long as TASK_CONGESTED remains set, requests can only be claimed by tasks woken from the backlog, and they are woken only as requests are freed, so when a task doesn't claim a request, no other task can ever get that request until TASK_CONGESTED is cleared. Each time this happens the number of available requests is decreased by one. With a sufficiently high workload and sufficiently low setting of max_slot (16 in the case where this was seen), TASK_CONGESTED can remain set for an extended period, and the above scenario (of a process being killed just as its task was woken) can repeat until no requests can be allocated. Then traffic stops. This patch addresses the problem by introducing a positive handover of a request from a completing task to a backlog task - the request is never freed when there is a backlog. When a task is woken it might not already have a request attached in which case it is *not* freed (as with current code) but is initialised (if needed) and used. If it isn't used it will eventually be freed by rpc_exit_task(). xprt_release() is enhanced to be able to correctly release an uninitialised request. Fixes: ba60eb25ff6b ("SUNRPC: Fix a livelock problem in the xprt->backlog queue") Signed-off-by: NeilBrown <neilb@suse.de> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Diffstat (limited to 'net/sunrpc/clnt.c')
-rw-r--r--net/sunrpc/clnt.c7
1 files changed, 0 insertions, 7 deletions
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index f555d335e910..42623d6b8f0e 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -1677,13 +1677,6 @@ call_reserveresult(struct rpc_task *task)
return;
}
- /*
- * Even though there was an error, we may have acquired
- * a request slot somehow. Make sure not to leak it.
- */
- if (task->tk_rqstp)
- xprt_release(task);
-
switch (status) {
case -ENOMEM:
rpc_delay(task, HZ >> 2);