> On Sep 8, 2019, at 11:19 AM, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote: > > 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? I'm looking at gss_unwrap_resp_integ(): 1971 auth->au_rslack = auth->au_verfsize + 2 + 1 + XDR_QUADLEN(mic.len); 1972 auth->au_ralign = auth->au_verfsize + 2; au_ralign now sets the alignment of the _start_ of the RPC message body. The MIC comes _after_ the RPC message body for krb5i. If Ben is off by one quad, that's not the MIC, which is typically 32 octets, isn't it? Maybe some variable-length data item in the returned file attributes is missing an XDR pad. -- Chuck Lever
