From 3dedbb5ca10ef13f25055776d2f6d9499d9ca1ba Mon Sep 17 00:00:00 2001 From: Jason Baron Date: Wed, 24 Sep 2014 18:08:04 +0000 Subject: rpc: Add -EPERM processing for xs_udp_send_request() If an iptables drop rule is added for an nfs server, the client can end up in a softlockup. Because of the way that xs_sendpages() is structured, the -EPERM is ignored since the prior bits of the packet may have been successfully queued and thus xs_sendpages() returns a non-zero value. Then, xs_udp_send_request() thinks that because some bits were queued it should return -EAGAIN. We then try the request again and again, resulting in cpu spinning. Reproducer: 1) open a file on the nfs server '/nfs/foo' (mounted using udp) 2) iptables -A OUTPUT -d -j DROP 3) write to /nfs/foo 4) close /nfs/foo 5) iptables -D OUTPUT -d -j DROP The softlockup occurs in step 4 above. The previous patch, allows xs_sendpages() to return both a sent count and any error values that may have occurred. Thus, if we get an -EPERM, return that to the higher level code. With this patch in place we can successfully abort the above sequence and avoid the softlockup. I also tried the above test case on an nfs mount on tcp and although the system does not softlockup, I still ended up with the 'hung_task' firing after 120 seconds, due to the i/o being stuck. The tcp case appears a bit harder to fix, since -EPERM appears to get ignored much lower down in the stack and does not propogate up to xs_sendpages(). This case is not quite as insidious as the softlockup and it is not addressed here. Reported-by: Yigong Lou Signed-off-by: Jason Baron Signed-off-by: Trond Myklebust --- net/sunrpc/clnt.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'net/sunrpc/clnt.c') diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c index 488ddeed9363..c4c60697589a 100644 --- a/net/sunrpc/clnt.c +++ b/net/sunrpc/clnt.c @@ -1913,6 +1913,7 @@ call_transmit_status(struct rpc_task *task) case -EHOSTDOWN: case -EHOSTUNREACH: case -ENETUNREACH: + case -EPERM: if (RPC_IS_SOFTCONN(task)) { xprt_end_transmit(task); rpc_exit(task, task->tk_status); @@ -2018,6 +2019,7 @@ call_status(struct rpc_task *task) case -EHOSTDOWN: case -EHOSTUNREACH: case -ENETUNREACH: + case -EPERM: if (RPC_IS_SOFTCONN(task)) { rpc_exit(task, status); break; -- cgit v1.2.3-55-g7522