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/xprtsock.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'net/sunrpc/xprtsock.c') diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c index 7d9ea6b7113d..02603ec2460a 100644 --- a/net/sunrpc/xprtsock.c +++ b/net/sunrpc/xprtsock.c @@ -644,6 +644,10 @@ static int xs_udp_send_request(struct rpc_task *task) dprintk("RPC: xs_udp_send_request(%u) = %d\n", xdr->len - req->rq_bytes_sent, status); + /* firewall is blocking us, don't return -EAGAIN or we end up looping */ + if (status == -EPERM) + goto process_status; + if (sent > 0 || status == 0) { req->rq_xmit_bytes_sent += sent; if (sent >= req->rq_slen) @@ -652,6 +656,7 @@ static int xs_udp_send_request(struct rpc_task *task) status = -EAGAIN; } +process_status: switch (status) { case -ENOTSOCK: status = -ENOTCONN; @@ -667,6 +672,7 @@ static int xs_udp_send_request(struct rpc_task *task) case -ENOBUFS: case -EPIPE: case -ECONNREFUSED: + case -EPERM: /* When the server has died, an ICMP port unreachable message * prompts ECONNREFUSED. */ clear_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags); -- cgit v1.2.3-55-g7522