3dedbb5ca1
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> |
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.. | ||
auth_gss | ||
xprtrdma | ||
addr.c | ||
auth_generic.c | ||
auth_null.c | ||
auth_unix.c | ||
auth.c | ||
backchannel_rqst.c | ||
bc_svc.c | ||
cache.c | ||
clnt.c | ||
Kconfig | ||
Makefile | ||
netns.h | ||
rpc_pipe.c | ||
rpcb_clnt.c | ||
sched.c | ||
socklib.c | ||
stats.c | ||
sunrpc_syms.c | ||
sunrpc.h | ||
svc_xprt.c | ||
svc.c | ||
svcauth_unix.c | ||
svcauth.c | ||
svcsock.c | ||
sysctl.c | ||
timer.c | ||
xdr.c | ||
xprt.c | ||
xprtsock.c |