linux-kernel - Re: [PATCH] fs/nfsd: Delete invalid assignment statements in nfsd4_decode_exchange

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Date:   Sun, 22 Jul 2018 19:08:09 +0000
From:   Trond Myklebust <trondmy@...merspace.com>
To:     "chuck.lever@...cle.com" <chuck.lever@...cle.com>
CC:     "bfields@...ldses.org" <bfields@...ldses.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nixiaoming@...wei.com" <nixiaoming@...wei.com>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "jlayton@...nel.org" <jlayton@...nel.org>
Subject: Re: [PATCH] fs/nfsd: Delete invalid assignment statements in
 nfsd4_decode_exchange_id

On Sun, 2018-07-22 at 15:01 -0400, Chuck Lever wrote:
> > On Jul 22, 2018, at 2:33 PM, Trond Myklebust <
> > trondmy@...merspace.com> wrote:
> > 
> > On Sun, 2018-07-22 at 14:12 -0400, Chuck Lever wrote:
> > > > On Jul 22, 2018, at 4:50 AM, nixiaoming <nixiaoming@...wei.com>
> > > > wrote:
> > > > 
> > > > dummy = be32_to_cpup(p++);
> > > > dummy = be32_to_cpup(p++);
> > > > Assigning value to "dummy" here, but that stored value
> > > > is overwritten before it can be used.
> > > > 
> > > > delete invalid assignment statements in
> > > > nfsd4_decode_exchange_id
> > > > 
> > > > Signed-off-by: n00202754 <nixiaoming@...wei.com>
> > > > ---
> > > > fs/nfsd/nfs4xdr.c | 4 ++--
> > > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> > > > index a96843c..8e78541 100644
> > > > --- a/fs/nfsd/nfs4xdr.c
> > > > +++ b/fs/nfsd/nfs4xdr.c
> > > > @@ -1392,8 +1392,8 @@ nfsd4_decode_exchange_id(struct
> > > > nfsd4_compoundargs *argp,
> > > > 
> > > > 		/* ssp_window and ssp_num_gss_handles */
> > > > 		READ_BUF(8);
> > > > -		dummy = be32_to_cpup(p++);
> > > > -		dummy = be32_to_cpup(p++);
> > > > +		be32_to_cpup(p++);
> > > > +		be32_to_cpup(p++);
> > > 
> > > If these values are not used, what's the point of byte swapping
> > > them?
> > > Surely "p += 2;" should be enough.
> > > 
> > > 
> > > > 		break;
> > > > 	default:
> > > > 		goto xdr_error;
> > 
> > Given that the value of 'p' isn't used either, why not just delete
> > those two lines altogether?
> 
> Sounds OK, READ_BUF is tracking progress through the buffer,
> and it already updates "p" as a side-effect.
> 
> Might there be some nearby instances of open-coded "p" updates
> that could also be removed, for similar reasons?
> 

Probably, yes. I believe that we've said before (and Bruce agreed at
the time) that we should get rid of READ_BUF() in knfsd as it tends to
obfuscate these assignments to 'p'. Does anyone have any free cycles to
work on that?

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@...merspace.com