Re: [PATCH v2 19/19] sunrpc: Disable splice for krb5i

Jeff Layton
2017-06-17T10:01:52Z

On Fri, 2017-06-16 at 11:22 -0400, Chuck Lever wrote:
> Running a multi-threaded 8KB fio test (70/30 mix), three or four out
> of twelve of the jobs fail when using krb5i. The failure is an EIO
> on a read.
>
> Troubleshooting confirmed the EIO results when the client fails to
> verify the MIC of an NFS READ reply. Bruce suggested the problem
> could be due to the data payload changing between the time the
> reply's MIC was computed on the server and the time the reply was
> actually sent.
>
> krb5p gets around this problem by disabling RQ_SPLICE_OK.
>
> "iozone -i0 -i1 -s128m -y1k -az -I", export is tmpfs, mount is
> sec=krb5i,vers=3,proto=rdma. The important numbers are the
> read / reread column.
>
> Here's without the RQ_SPLICE_OK patch:
>
> kB reclen write rewrite read reread
> 131072 1 7546 7929 8396 8267
> 131072 2 14375 14600 15843 15639
> 131072 4 19280 19248 21303 21410
> 131072 8 32350 31772 35199 34883
> 131072 16 36748 37477 49365 51706
> 131072 32 55669 56059 57475 57389
> 131072 64 74599 75190 74903 75550
> 131072 128 99810 101446 102828 102724
> 131072 256 122042 122612 124806 125026
> 131072 512 137614 138004 141412 141267
> 131072 1024 146601 148774 151356 151409
> 131072 2048 180684 181727 293140 292840
> 131072 4096 206907 207658 552964 549029
> 131072 8192 223982 224360 454493 473469
> 131072 16384 228927 228390 654734 632607
>
> And here's with it:
>
> kB reclen write rewrite read reread
> 131072 1 7700 7365 7958 8011
> 131072 2 13211 13303 14937 14414
> 131072 4 19001 19265 20544 20657
> 131072 8 30883 31097 34255 33566
> 131072 16 36868 34908 51499 49944
> 131072 32 56428 55535 58710 56952
> 131072 64 73507 74676 75619 74378
> 131072 128 100324 101442 103276 102736
> 131072 256 122517 122995 124639 124150
> 131072 512 137317 139007 140530 140830
> 131072 1024 146807 148923 151246 151072
> 131072 2048 179656 180732 292631 292034
> 131072 4096 206216 208583 543355 541951
> 131072 8192 223738 224273 494201 489372
> 131072 16384 229313 229840 691719 668427
>
> I would say that there is not much difference in this test.
>
> For good measure, here's the same test with sec=krb5p:
>
> kB reclen write rewrite read reread
> 131072 1 5982 5881 6137 6218
> 131072 2 10216 10252 10850 10932
> 131072 4 12236 12575 15375 15526
> 131072 8 15461 15462 23821 22351
> 131072 16 25677 25811 27529 27640
> 131072 32 31903 32354 34063 33857
> 131072 64 42989 43188 45635 45561
> 131072 128 52848 53210 56144 56141
> 131072 256 59123 59214 62691 62933
> 131072 512 63140 63277 66887 67025
> 131072 1024 65255 65299 69213 69140
> 131072 2048 76454 76555 133767 133862
> 131072 4096 84726 84883 251925 250702
> 131072 8192 89491 89482 270821 276085
> 131072 16384 91572 91597 361768 336868
>
> BugLink: https://bugzilla.linux-nfs.org/show_bug.cgi?id=307
> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> ---
> net/sunrpc/auth_gss/svcauth_gss.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
> index a54a7a3..ab329f4 100644
> --- a/net/sunrpc/auth_gss/svcauth_gss.c
> +++ b/net/sunrpc/auth_gss/svcauth_gss.c
> @@ -838,6 +838,8 @@ u32 svcauth_gss_flavor(struct auth_domain *dom)
> struct xdr_netobj mic;
> struct xdr_buf integ_buf;
>
> + clear_bit(RQ_SPLICE_OK, &rqstp->rq_flags);
> +
> /* Did we already verify the signature on the original pass through? */
> if (rqstp->rq_deferred)
> return 0;
>
> --
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This seems like the right thing to do, IMO. It's nice to avoid copies
where we can, but this is just one of the places where we can't, at
least with the way things stand now. It is a pity we don't have a way to
CoW these things though.

Reviewed-by: Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>