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authorJason Baron <jbaron@akamai.com>2014-09-24 22:08:04 +0400
committerTrond Myklebust <trond.myklebust@primarydata.com>2014-09-25 07:13:46 +0400
commit3dedbb5ca10ef13f25055776d2f6d9499d9ca1ba (patch)
tree20484da7a5b19d2e1afa5777a01fe608b5a89214 /net/sunrpc/clnt.c
parentf279cd008fc9742f5ec294d9b8a793a7a0b163ef (diff)
downloadlinux-3dedbb5ca10ef13f25055776d2f6d9499d9ca1ba.tar.xz
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 <nfs server ip> -j DROP 3) write to /nfs/foo 4) close /nfs/foo 5) iptables -D OUTPUT -d <nfs server ip> -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 <ylou@akamai.com> Signed-off-by: Jason Baron <jbaron@akamai.com> Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Diffstat (limited to 'net/sunrpc/clnt.c')
-rw-r--r--net/sunrpc/clnt.c2
1 files changed, 2 insertions, 0 deletions
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;