| Message ID | 1321965938.7645.13.camel@lade.trondhjem.org |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | David Miller |
| Headers | show |
On 22/11/11 12:45, Trond Myklebust wrote: > On Tue, 2011-11-22 at 12:34 +0000, Andrew Cooper wrote: >> On 22/11/11 12:22, Trond Myklebust wrote: >>> On Tue, 2011-11-22 at 12:16 +0000, Andrew Cooper wrote: >>>> On 22/11/11 12:10, Trond Myklebust wrote: >>>>> On Tue, 2011-11-22 at 12:02 +0000, Andrew Cooper wrote: >>>>>> On 22/11/11 11:38, Trond Myklebust wrote: >>>>>>> On Mon, 2011-11-21 at 18:14 +0000, Andrew Cooper wrote: >>>>>>>> Following some debugging, I believe that the attached patch fixes the >>>>>>>> problem. >>>>>>>> >>>>>>>> Simply returning EAGAIN is not sufficient, as the task does not get >>>>>>>> requeued, and times out 13 seconds later (as per our mount options). >>>>>>>> Setting the SOCK_ASYNC_NOSPACE bit causes the requeue to happen. >>>>>>>> >>>>>>>> I realize that this is a gross hack and I should probably not be using >>>>>>>> SOCK_ASYNC_NOSPACE in that way. Is there a better way to achieve the >>>>>>>> same solution? >>>>>>>> >>>>>>> What you are doing will cause the request to be put to sleep with no >>>>>>> guarantee that it will ever be woken up. Why would we want to do that if >>>>>>> there is no report of a tcp window/buffer space congestion? >>>>>> But the reason we get to this code is because there was a report of >>>>>> space collision. What would you suggest instead? Changing >>>>>> xs_{tcp,udp}_send_request() to retry in this case would defeat the point >>>>>> of having xs_nospace(). >>>>> I suggest doing absolutely nothing: do what you originally proposed, >>>>> which is to report the EAGAIN so that the client state machine retries >>>>> the socket write. >>>>> >>>>> My point is that this is a context which is _not_ atomic with the >>>>> original report of tcp window/buffer space congestion. There are no >>>>> locks or anything else that will guarantee that the congestion still >>>>> exists, and the fact that the SOCK_ASYNC_NOSPACE flag is now clear >>>>> indicates that this is the case. >>>>> The whole purpose of xs_nospace() is to wait until a congestion >>>>> condition clears. If the congestion clears before we get here, then we >>>>> have no reason to do anything special other than retry. >>>>> >>>>> Trond >>>> I am slightly confused as to what you mean now. >>>> >>>> When you take out the if(test_bit test and always set ret to EAGAIN and >>>> requeue the request, the next time it wakes up is when it is killed due >>>> to timeout. This results in substantially worse effects for the >>>> userspace, as the NFS session is killed. >>> What is putting the request to sleep? It should be awake when it enters >>> xs_nospace(), and nothing in or after that function should be putting it >>> to sleep until we've retried with call_transmit(). >>> >> I presume it is the call to xprt_wait_for_buffer_space() which calls >> rpc_sleep_on(). There is xs_tcp_write_space which appears to wake it up >> based on sk->sk_write_space which is triggered on the sock gaining more >> space, which has already happened in this specific case. > That call should only happen if we have to wait for congestion (i.e. if > SOCK_ASYNC_NOSPACE is set). > > Please can you test if the following patch fixes the problem. > > Cheers > Trond Yup - this works and seems like a rather more elegant solution. Thanks for all you help - I have been chasing this bug on and off since the middle of May. > 8<--------------------------------------------------------------------- > From 729b3861d9a2820735b648a044d558315bc9c9db Mon Sep 17 00:00:00 2001 > From: Trond Myklebust <Trond.Myklebust@netapp.com> > Date: Tue, 22 Nov 2011 14:44:28 +0200 > Subject: [PATCH] SUNRPC: Ensure we return EAGAIN in xs_nospace if congestion > is cleared > > By returning '0' instead of 'EAGAIN' when the tests in xs_nospace() fail > to find evidence of socket congestion, we are making the RPC engine believe > that the message was incompletely sent, and so it disconnects the socket > instead of just retrying the send. > > The bug appears to have been introduced by commit > 5e3771ce2d6a69e10fcc870cdf226d121d868491 (SUNRPC: Ensure that xs_nospace > return values are propagated). > > Reported-by: Andrew Cooper <andrew.cooper3@citrix.com> > Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com> Tested-by: Andrew Cooper <andrew.cooper3@citrix.com> > Cc: stable@vger.kernel.org [>= 2.6.30] > --- > net/sunrpc/xprtsock.c | 3 +-- > 1 files changed, 1 insertions(+), 2 deletions(-) > > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c > index 2d78d95..55472c4 100644 > --- a/net/sunrpc/xprtsock.c > +++ b/net/sunrpc/xprtsock.c > @@ -496,7 +496,7 @@ static int xs_nospace(struct rpc_task *task) > struct rpc_rqst *req = task->tk_rqstp; > struct rpc_xprt *xprt = req->rq_xprt; > struct sock_xprt *transport = container_of(xprt, struct sock_xprt, xprt); > - int ret = 0; > + int ret = -EAGAIN; > > dprintk("RPC: %5u xmit incomplete (%u left of %u)\n", > task->tk_pid, req->rq_slen - req->rq_bytes_sent, > @@ -508,7 +508,6 @@ static int xs_nospace(struct rpc_task *task) > /* Don't race with disconnect */ > if (xprt_connected(xprt)) { > if (test_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags)) { > - ret = -EAGAIN; > /* > * Notify TCP that we're limited by the application > * window size
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c index 2d78d95..55472c4 100644 --- a/net/sunrpc/xprtsock.c +++ b/net/sunrpc/xprtsock.c @@ -496,7 +496,7 @@ static int xs_nospace(struct rpc_task *task) struct rpc_rqst *req = task->tk_rqstp; struct rpc_xprt *xprt = req->rq_xprt; struct sock_xprt *transport = container_of(xprt, struct sock_xprt, xprt); - int ret = 0; + int ret = -EAGAIN; dprintk("RPC: %5u xmit incomplete (%u left of %u)\n", task->tk_pid, req->rq_slen - req->rq_bytes_sent, @@ -508,7 +508,6 @@ static int xs_nospace(struct rpc_task *task) /* Don't race with disconnect */ if (xprt_connected(xprt)) { if (test_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags)) { - ret = -EAGAIN; /* * Notify TCP that we're limited by the application * window size