Re: [PATCH RESEND] svcrdma: handle rdma read with a non-zero initial page offset

[Doug Ledford <dledford@redhat.com>]

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On 09/28/2015 05:46 PM, Steve Wise wrote:
> The server rdma_read_chunk_lcl() and rdma_read_chunk_frmr() functions
> were not taking into account the initial page_offset when determining
> the rdma read length.  This resulted in a read who's starting address
> and length exceeded the base/bounds of the frmr.
> 
> Most work loads don't tickle this bug apparently, but one test hit it
> every time: building the linux kernel on a 16 core node with 'make -j
> 16 O=/mnt/0' where /mnt/0 is a ramdisk mounted via NFSRDMA.
> 
> This bug seems to only be tripped with devices having small fastreg page
> list depths.  I didn't see it with mlx4, for instance.

Bruce, what's you're take on this?  Do you want to push this through or
would you care if I push it through my tree?

> Fixes: 0bf4828983df ('svcrdma: refactor marshalling logic')
> Signed-off-by: Steve Wise <swise@opengridcomputing.com>
> Tested-by: Chuck Lever <chuck.lever@oracle.com>
> ---
> 
>  net/sunrpc/xprtrdma/svc_rdma_recvfrom.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> index cb51742..5f6ca47 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> @@ -136,7 +136,8 @@ int rdma_read_chunk_lcl(struct svcxprt_rdma *xprt,
>  	ctxt->direction = DMA_FROM_DEVICE;
>  	ctxt->read_hdr = head;
>  	pages_needed = min_t(int, pages_needed, xprt->sc_max_sge_rd);
> -	read = min_t(int, pages_needed << PAGE_SHIFT, rs_length);
> +	read = min_t(int, (pages_needed << PAGE_SHIFT) - *page_offset,
> +		     rs_length);
>  
>  	for (pno = 0; pno < pages_needed; pno++) {
>  		int len = min_t(int, rs_length, PAGE_SIZE - pg_off);
> @@ -235,7 +236,8 @@ int rdma_read_chunk_frmr(struct svcxprt_rdma *xprt,
>  	ctxt->direction = DMA_FROM_DEVICE;
>  	ctxt->frmr = frmr;
>  	pages_needed = min_t(int, pages_needed, xprt->sc_frmr_pg_list_len);
> -	read = min_t(int, pages_needed << PAGE_SHIFT, rs_length);
> +	read = min_t(int, (pages_needed << PAGE_SHIFT) - *page_offset,
> +		     rs_length);
>  
>  	frmr->kva = page_address(rqstp->rq_arg.pages[pg_no]);
>  	frmr->direction = DMA_FROM_DEVICE;
> 
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-- 
Doug Ledford <dledford@redhat.com>
              GPG KeyID: 0E572FDD



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