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

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Date:   Mon, 23 Jul 2018 02:16:49 +0000
From:   Nixiaoming <nixiaoming@...wei.com>
To:     Trond Myklebust <trondmy@...merspace.com>,
        "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>,
        "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 Mon, Jul 23, 2018 at 3:08 AM, Trond Myklebust wrote:
>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
>
>

Thank you for your review, 
I will update the patch as soon as possible based on your comments.

Thanks