Re: [PATCH] Fix regression in NFSRDMA server

[Tom Tucker <tom@xxxxxxxxxxxxxxxxxxxxx>]

Hi Bruce,

On 3/27/14 9:08 PM, J. Bruce Fields wrote:
> On Tue, Mar 25, 2014 at 03:14:57PM -0500, Steve Wise wrote:
> > From: Tom Tucker <tom@xxxxxx>
> >
> > The server regression was caused by the addition of rq_next_page
> > (afc59400d6c65bad66d4ad0b2daf879cbff8e23e). There were a few places that
> > were missed with the update of the rq_respages array.
> Apologies.  (But, it could happen again--could we set up some regular
> testing?  It doesn't have to be anything fancy, just cthon over
> rdma--really, just read and write over rdma--would probably catch a
> lot.)

I think Chelsio is going to be adding some NFSRDMA regression testing to 
their system test.

> Also: I don't get why all these rq_next_page initializations are
> required.  Why isn't the initialization at the top of svc_process()
> enough?  Is rdma using it before we get to that point?  The only use of
> it I see off hand is in the while loop that you're deleting.

I didn't apply tremendous deductive powers here, I just added updates to 
rq_next_page wherever the transport messed with rq_respages. That said, 
NFS WRITE is likely the culprit since the write is completed as a deferral 
and therefore the request doesn't go through svc_process, so if 
rq_next_page is bogus, the cleanup will free/re-use pages that are 
actually in use by the transport.

Tom
> --b.
>
> > Signed-off-by: Tom Tucker <tom@xxxxxx>
> > Tested-by: Steve Wise <swise@xxxxxx>
> > ---
> >
> >   net/sunrpc/xprtrdma/svc_rdma_recvfrom.c |   12 ++++--------
> >   net/sunrpc/xprtrdma/svc_rdma_sendto.c   |    1 +
> >   2 files changed, 5 insertions(+), 8 deletions(-)
> >
> > diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> > index 0ce7552..8d904e4 100644
> > --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> > +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> > @@ -90,6 +90,7 @@ static void rdma_build_arg_xdr(struct svc_rqst *rqstp,
> >   		sge_no++;
> >   	}
> >   	rqstp->rq_respages = &rqstp->rq_pages[sge_no];
> > +	rqstp->rq_next_page = rqstp->rq_respages + 1;
> >   
> >   	/* We should never run out of SGE because the limit is defined to
> >   	 * support the max allowed RPC data length
> > @@ -169,6 +170,7 @@ static int map_read_chunks(struct svcxprt_rdma *xprt,
> >   		 */
> >   		head->arg.pages[page_no] = rqstp->rq_arg.pages[page_no];
> >   		rqstp->rq_respages = &rqstp->rq_arg.pages[page_no+1];
> > +		rqstp->rq_next_page = rqstp->rq_respages + 1;
> >   
> >   		byte_count -= sge_bytes;
> >   		ch_bytes -= sge_bytes;
> > @@ -276,6 +278,7 @@ static int fast_reg_read_chunks(struct svcxprt_rdma *xprt,
> >   
> >   	/* rq_respages points one past arg pages */
> >   	rqstp->rq_respages = &rqstp->rq_arg.pages[page_no];
> > +	rqstp->rq_next_page = rqstp->rq_respages + 1;
> >   
> >   	/* Create the reply and chunk maps */
> >   	offset = 0;
> > @@ -520,13 +523,6 @@ next_sge:
> >   	for (ch_no = 0; &rqstp->rq_pages[ch_no] < rqstp->rq_respages; ch_no++)
> >   		rqstp->rq_pages[ch_no] = NULL;
> >   
> > -	/*
> > -	 * Detach res pages. If svc_release sees any it will attempt to
> > -	 * put them.
> > -	 */
> > -	while (rqstp->rq_next_page != rqstp->rq_respages)
> > -		*(--rqstp->rq_next_page) = NULL;
> > -
> >   	return err;
> >   }
> >   
> > @@ -550,7 +546,7 @@ static int rdma_read_complete(struct svc_rqst *rqstp,
> >   
> >   	/* rq_respages starts after the last arg page */
> >   	rqstp->rq_respages = &rqstp->rq_arg.pages[page_no];
> > -	rqstp->rq_next_page = &rqstp->rq_arg.pages[page_no];
> > +	rqstp->rq_next_page = rqstp->rq_respages + 1;
> >   
> >   	/* Rebuild rq_arg head and tail. */
> >   	rqstp->rq_arg.head[0] = head->arg.head[0];
> > diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
> > index c1d124d..11e90f8 100644
> > --- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
> > +++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
> > @@ -625,6 +625,7 @@ static int send_reply(struct svcxprt_rdma *rdma,
> >   		if (page_no+1 >= sge_no)
> >   			ctxt->sge[page_no+1].length = 0;
> >   	}
> > +	rqstp->rq_next_page = rqstp->rq_respages + 1;
> >   	BUG_ON(sge_no > rdma->sc_max_sge);
> >   	memset(&send_wr, 0, sizeof send_wr);
> >   	ctxt->wr_op = IB_WR_SEND;
> --
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