On Sun, 2019-09-08 at 07:39 -0400, Benjamin Coddington wrote: > On 6 Sep 2019, at 16:50, Chuck Lever wrote: > > > > On Sep 6, 2019, at 4:47 PM, Jason L Tibbitts III < > > > tibbs@xxxxxxxxxxx> > > > wrote: > > > > > > > > > > > "JBF" == J Bruce Fields <bfields@xxxxxxxxxxxx> writes: > > > > > > JBF> Those readdir changes were client-side, right? Based on > > > that > > > I'd > > > JBF> been assuming a client bug, but maybe it'd be worth getting > > > a > > > full > > > JBF> packet capture of the readdir reply to make sure it's legit. > > > > > > I have been working with bcodding on IRC for the past couple of > > > days > > > on > > > this. Fortunately I was able to come up with way to fill up a > > > directory > > > in such a way that it will fail with certainty and as a bonus > > > doesn't > > > include any user data so I can feel OK about sharing packet > > > captures. > > > I > > > have a capture alongside a kernel trace of the problematic > > > operation > > > in > > > https://www.math.uh.edu/~tibbs/nfs/. Not that I can > > > particularly > > > tell > > > anything useful from that, but bcodding says that it seems to > > > point > > > to > > > some issue in sunrpc. > > > > > > And because I can easily reproduce this and I was able to do a > > > bisect: > > > > > > 2c94b8eca1a26cd46010d6e73a23da5f2e93a19d is the first bad commit > > > commit 2c94b8eca1a26cd46010d6e73a23da5f2e93a19d > > > Author: Chuck Lever <chuck.lever@xxxxxxxxxx> > > > Date: Mon Feb 11 11:25:41 2019 -0500 > > > > > > SUNRPC: Use au_rslack when computing reply buffer size > > > > > > au_rslack is significantly smaller than (au_cslack << 2). > > > Using > > > that value results in smaller receive buffers. In some cases > > > this > > > eliminates an extra segment in Reply chunks (RPC/RDMA). > > > > > > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> > > > Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx> > > > > > > :040000 040000 d4d1ce2fbe0035c5bd9df976b8c448df85dcb505 > > > 7011a792dfe72ff9cd70d66e45d353f3d7817e3e M net > > > > > > But of course, I can't say whether this is the actual bad commit > > > or > > > whether it just introduced a behavior change which alters the > > > conditions > > > under which the problem appears. > > > > The first place I'd start looking is the XDR constants at the head > > of > > fs/nfs/nfs4xdr.c > > having to do with READDIR. > > > > The report of behavior changes with the use of krb5p also makes > > this > > commit plausible. > > After sprinkling the printk's, we're coming up one word short in the > receive > buffer. I think we're not accounting for the xdr pad of buf->pages > for > NFS4 > readdir -- but I need to check the RFCs. Anyone know if v4 READDIR > results > have to be aligned? > > Also need to check just why krb5i is the only auth that cares.. > I'm not seeing that. If you look at commit 02ef04e432ba, you'll see that Chuck did add a 'padding term' to decode_readdir_maxsz in the NFSv4 case. The other thing to remember is that a readdir 'dirlist4' entry is always word aligned (irrespective of the length of the filename), so there is no padding that needs to be taken into account. I think we probably rather want to look at how auth->au_ralign is being calculated for the case of krb5i. I'm really not understanding why auth->au_ralign should not take into account the presence of the mic. Chuck? -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
