linux-kernel - Re: [PATCH] nfsd: Using guard() to simplify nfsd_cache

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <148c69b4-4cf7-4112-97e8-6a5c23505638@suswa.mountain>
Date: Mon, 23 Jun 2025 18:47:28 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Su Hui <suhui@...china.com>
Cc: chuck.lever@...cle.com, jlayton@...nel.org, neil@...wn.name,
	okorniev@...hat.com, Dai.Ngo@...cle.com, tom@...pey.com,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] nfsd: Using guard() to simplify nfsd_cache_lookup()

On Mon, Jun 23, 2025 at 08:22:27PM +0800, Su Hui wrote:
> Using guard() to replace *unlock* label. guard() makes lock/unlock code
> more clear. Change the order of the code to let all lock code in the
> same scope. No functional changes.
> 
> Signed-off-by: Su Hui <suhui@...china.com>
> ---
>  fs/nfsd/nfscache.c | 99 ++++++++++++++++++++++------------------------
>  1 file changed, 48 insertions(+), 51 deletions(-)
> 
> diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
> index ba9d326b3de6..2d92adf3e6b0 100644
> --- a/fs/nfsd/nfscache.c
> +++ b/fs/nfsd/nfscache.c
> @@ -489,7 +489,7 @@ int nfsd_cache_lookup(struct svc_rqst *rqstp, unsigned int start,
>  
>  	if (type == RC_NOCACHE) {
>  		nfsd_stats_rc_nocache_inc(nn);
> -		goto out;
> +		return rtn;
>  	}
>  
>  	csum = nfsd_cache_csum(&rqstp->rq_arg, start, len);
> @@ -500,64 +500,61 @@ int nfsd_cache_lookup(struct svc_rqst *rqstp, unsigned int start,
>  	 */
>  	rp = nfsd_cacherep_alloc(rqstp, csum, nn);
>  	if (!rp)
> -		goto out;
> +		return rtn;
>  
>  	b = nfsd_cache_bucket_find(rqstp->rq_xid, nn);
> -	spin_lock(&b->cache_lock);
> -	found = nfsd_cache_insert(b, rp, nn);
> -	if (found != rp)
> -		goto found_entry;
> -	*cacherep = rp;
> -	rp->c_state = RC_INPROG;
> -	nfsd_prune_bucket_locked(nn, b, 3, &dispose);
> -	spin_unlock(&b->cache_lock);
> +	scoped_guard(spinlock, &b->cache_lock) {
> +		found = nfsd_cache_insert(b, rp, nn);
> +		if (found == rp) {
> +			*cacherep = rp;
> +			rp->c_state = RC_INPROG;
> +			nfsd_prune_bucket_locked(nn, b, 3, &dispose);
> +			goto out;

It took me a while to figure out why we've added a goto here.  In the
original code this "goto out;" was a "spin_unlock(&b->cache_lock);".
The spin_unlock() is more readable because you can immediately see that
it's trying to drop the lock where a "goto out;" is less obvious about
the intention.

I think this patch works fine, but I'm not sure it's an improvement.

regards,
dan carpenter

> +		}
> +		/* We found a matching entry which is either in progress or done. */
> +		nfsd_reply_cache_free_locked(NULL, rp, nn);
> +		nfsd_stats_rc_hits_inc(nn);
> +		rtn = RC_DROPIT;
> +		rp = found;
> +
> +		/* Request being processed */
> +		if (rp->c_state == RC_INPROG)
> +			goto out_trace;
> +
> +		/* From the hall of fame of impractical attacks:
> +		 * Is this a user who tries to snoop on the cache?
> +		 */
> +		rtn = RC_DOIT;
> +		if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && rp->c_secure)
> +			goto out_trace;
>  
> +		/* Compose RPC reply header */
> +		switch (rp->c_type) {
> +		case RC_NOCACHE:
> +			break;
> +		case RC_REPLSTAT:
> +			xdr_stream_encode_be32(&rqstp->rq_res_stream, rp->c_replstat);
> +			rtn = RC_REPLY;
> +			break;
> +		case RC_REPLBUFF:
> +			if (!nfsd_cache_append(rqstp, &rp->c_replvec))
> +				return rtn; /* should not happen */
> +			rtn = RC_REPLY;
> +			break;
> +		default:
> +			WARN_ONCE(1, "nfsd: bad repcache type %d\n", rp->c_type);
> +		}
> +
> +out_trace:
> +		trace_nfsd_drc_found(nn, rqstp, rtn);
> +		return rtn;
> +	}
> +out:
>  	nfsd_cacherep_dispose(&dispose);
>  
>  	nfsd_stats_rc_misses_inc(nn);
>  	atomic_inc(&nn->num_drc_entries);
>  	nfsd_stats_drc_mem_usage_add(nn, sizeof(*rp));
> -	goto out;
> -
> -found_entry:
> -	/* We found a matching entry which is either in progress or done. */
> -	nfsd_reply_cache_free_locked(NULL, rp, nn);
> -	nfsd_stats_rc_hits_inc(nn);
> -	rtn = RC_DROPIT;
> -	rp = found;
> -
> -	/* Request being processed */
> -	if (rp->c_state == RC_INPROG)
> -		goto out_trace;
> -
> -	/* From the hall of fame of impractical attacks:
> -	 * Is this a user who tries to snoop on the cache? */
> -	rtn = RC_DOIT;
> -	if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && rp->c_secure)
> -		goto out_trace;
> -
> -	/* Compose RPC reply header */
> -	switch (rp->c_type) {
> -	case RC_NOCACHE:
> -		break;
> -	case RC_REPLSTAT:
> -		xdr_stream_encode_be32(&rqstp->rq_res_stream, rp->c_replstat);
> -		rtn = RC_REPLY;
> -		break;
> -	case RC_REPLBUFF:
> -		if (!nfsd_cache_append(rqstp, &rp->c_replvec))
> -			goto out_unlock; /* should not happen */
> -		rtn = RC_REPLY;
> -		break;
> -	default:
> -		WARN_ONCE(1, "nfsd: bad repcache type %d\n", rp->c_type);
> -	}
> -
> -out_trace:
> -	trace_nfsd_drc_found(nn, rqstp, rtn);
> -out_unlock:
> -	spin_unlock(&b->cache_lock);
> -out:
>  	return rtn;
>  }
>  
> -- 
> 2.30.2
>