Re: [PATCH v4 07/30] xprtrdma: Fix ri_max_segs and the result of ro_maxpages

[Anna Schumaker <schumaker.anna@gmail.com>]

Hi Chuck,

On Mon, 2018-12-17 at 11:39 -0500, Chuck Lever wrote:
> With certain combinations of krb5i/p, MR size, and r/wsize, I/O can
> fail with EMSGSIZE. This is because the calculated value of
> ri_max_segs (the max number of MRs per RPC) exceeded
> RPCRDMA_MAX_HDR_SEGS, which caused Read or Write list encoding to
> walk off the end of the transport header.
> 
> Once that was addressed, the ro_maxpages result has to be corrected
> to account for the number of MRs needed for Reply chunks, which is
> 2 MRs smaller than a normal Read or Write chunk.
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  net/sunrpc/xprtrdma/fmr_ops.c   |    7 +++++--
>  net/sunrpc/xprtrdma/frwr_ops.c  |    7 +++++--
>  net/sunrpc/xprtrdma/transport.c |    6 ++++--
>  3 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/fmr_ops.c b/net/sunrpc/xprtrdma/fmr_ops.c
> index 7f5632c..78a0224 100644
> --- a/net/sunrpc/xprtrdma/fmr_ops.c
> +++ b/net/sunrpc/xprtrdma/fmr_ops.c
> @@ -176,7 +176,10 @@ enum {
>  
>  	ia->ri_max_segs = max_t(unsigned int, 1, RPCRDMA_MAX_DATA_SEGS /
>  				RPCRDMA_MAX_FMR_SGES);
> -	ia->ri_max_segs += 2;	/* segments for head and tail buffers */
> +	/* Reply chunks require segments for head and tail buffers */
> +	ia->ri_max_segs += 2;
> +	if (ia->ri_max_segs > RPCRDMA_MAX_HDR_SEGS)
> +		ia->ri_max_segs = RPCRDMA_MAX_HDR_SEGS;
>  	return 0;
>  }
>  
> @@ -186,7 +189,7 @@ enum {
>  fmr_op_maxpages(struct rpcrdma_xprt *r_xprt)
>  {
>  	return min_t(unsigned int, RPCRDMA_MAX_DATA_SEGS,
> -		     RPCRDMA_MAX_HDR_SEGS * RPCRDMA_MAX_FMR_SGES);
> +		     (ia->ri_max_segs - 2) * RPCRDMA_MAX_FMR_SGES);

ia isn't defined in this function.  Should that be r_xprt->rx_ia.ri_max_segs
instead?

Thanks,
Anna

>  }
>  
>  /* Use the ib_map_phys_fmr() verb to register a memory region
> diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
> index 27222c0..f587e44 100644
> --- a/net/sunrpc/xprtrdma/frwr_ops.c
> +++ b/net/sunrpc/xprtrdma/frwr_ops.c
> @@ -244,7 +244,10 @@
>  
>  	ia->ri_max_segs = max_t(unsigned int, 1, RPCRDMA_MAX_DATA_SEGS /
>  				ia->ri_max_frwr_depth);
> -	ia->ri_max_segs += 2;	/* segments for head and tail buffers */
> +	/* Reply chunks require segments for head and tail buffers */
> +	ia->ri_max_segs += 2;
> +	if (ia->ri_max_segs > RPCRDMA_MAX_HDR_SEGS)
> +		ia->ri_max_segs = RPCRDMA_MAX_HDR_SEGS;
>  	return 0;
>  }
>  
> @@ -257,7 +260,7 @@
>  	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
>  
>  	return min_t(unsigned int, RPCRDMA_MAX_DATA_SEGS,
> -		     RPCRDMA_MAX_HDR_SEGS * ia->ri_max_frwr_depth);
> +		     (ia->ri_max_segs - 2) * ia->ri_max_frwr_depth);
>  }
>  
>  static void
> diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
> index a16296b..fbb14bf 100644
> --- a/net/sunrpc/xprtrdma/transport.c
> +++ b/net/sunrpc/xprtrdma/transport.c
> @@ -704,8 +704,10 @@
>   *	%-ENOTCONN if the caller should reconnect and call again
>   *	%-EAGAIN if the caller should call again
>   *	%-ENOBUFS if the caller should call again after a delay
> - *	%-EIO if a permanent error occurred and the request was not
> - *		sent. Do not try to send this message again.
> + *	%-EMSGSIZE if encoding ran out of buffer space. The request
> + *		was not sent. Do not try to send this message again.
> + *	%-EIO if an I/O error occurred. The request was not sent.
> + *		Do not try to send this message again.
>   */
>  static int
>  xprt_rdma_send_request(struct rpc_rqst *rqst)
>