On Wed, 09 Oct 2019, J. Bruce Fields wrote:
> On Wed, Oct 09, 2019 at 03:11:37PM -0400, Scott Mayhew wrote:
> > When running an nfs stress test, I see quite a few cached replies that
> > don't match up with the actual request. The first comment in
> > replay_matches_cache() makes sense, but the code doesn't seem to
> > match... fix it.
>
> Thanks, I'll apply. But I'm curious whether you're seeing any practical
> impact from this? I don't think it should matter.
Yes, the client is occasionally getting tied up into knots. It appears
to always be a REMOVE request getting a cached OPEN reply, and that
loops over and over. It seems like a client bug because when it
happens, the client sends an OPEN and immediately sends a REMOVE using
the same slot (bumping the seqid) without waiting for the OPEN reply.
The server replies with NFS4ERR_SEQ_MISORDERED, and the client
decrements the seqid and re-sends the REMOVE request. Then the server
sends the reply to the original OPEN and sends the cached OPEN reply in
response to all the subsequent REMOVE requests. I haven't had much luck
in tracking it down though...
-Scott
>
> --b.
>
> >
> > Fixes: 53da6a53e1d4 ("nfsd4: catch some false session retries")
> > Signed-off-by: Scott Mayhew <smayhew@xxxxxxxxxx>
> > ---
> > fs/nfsd/nfs4state.c | 15 ++++++++++-----
> > 1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index c65aeaa812d4..08f6eb2b73f8 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -3548,12 +3548,17 @@ static bool replay_matches_cache(struct svc_rqst *rqstp,
> > (bool)seq->cachethis)
> > return false;
> > /*
> > - * If there's an error than the reply can have fewer ops than
> > - * the call. But if we cached a reply with *more* ops than the
> > - * call you're sending us now, then this new call is clearly not
> > - * really a replay of the old one:
> > + * If there's an error then the reply can have fewer ops than
> > + * the call.
> > */
> > - if (slot->sl_opcnt < argp->opcnt)
> > + if (slot->sl_opcnt < argp->opcnt && !slot->sl_status)
> > + return false;
> > + /*
> > + * But if we cached a reply with *more* ops than the call you're
> > + * sending us now, then this new call is clearly not really a
> > + * replay of the old one:
> > + */
> > + if (slot->sl_opcnt > argp->opcnt)
> > return false;
> > /* This is the only check explicitly called by spec: */
> > if (!same_creds(&rqstp->rq_cred, &slot->sl_cred))
> > --
> > 2.17.2
