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

Chuck Lever
2017-06-16T15:22:54Z

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;