Re: [PATCH 2/4] lockd: eliminate duplicate nlmsvc_lookup_host call from nlmsvc_testlock

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Jul 15, 2008 at 02:48:11PM -0400, J. Bruce Fields wrote:
> From: Jeff Layton <jlayton@redhat.com>
> 
> nlmsvc_testlock calls nlmsvc_lookup_host to find a nlm_host struct. The
> callers of this functions, however, call nlmsvc_retrieve_args or
> nlm4svc_retrieve_args, which also return a nlm_host struct.
> 
> Change nlmsvc_testlock to take a host arg instead of calling
> nlmsvc_lookup_host itself and change the callers to pass a pointer to
> the nlm_host they've already found.
> 
> We take a reference to host in the place where nlmsvc_testlock()
> previous did a new lookup, so the reference counting is unchanged from
> before.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
> ---
>  fs/lockd/svc4proc.c         |    2 +-
>  fs/lockd/svclock.c          |   12 +++---------
>  fs/lockd/svcproc.c          |    2 +-
>  include/linux/lockd/lockd.h |    3 ++-
>  4 files changed, 7 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/lockd/svc4proc.c b/fs/lockd/svc4proc.c
> index 006a832..8cfb9da 100644
> --- a/fs/lockd/svc4proc.c
> +++ b/fs/lockd/svc4proc.c
> @@ -99,7 +99,7 @@ nlm4svc_proc_test(struct svc_rqst *rqstp, struct nlm_args *argp,
>  		return resp->status == nlm_drop_reply ? rpc_drop_reply :rpc_success;
>  
>  	/* Now check for conflicting locks */
> -	resp->status = nlmsvc_testlock(rqstp, file, &argp->lock, &resp->lock, &resp->cookie);
> +	resp->status = nlmsvc_testlock(rqstp, file, host, &argp->lock, &resp->lock, &resp->cookie);
>  	if (resp->status == nlm_drop_reply)
>  		rc = rpc_drop_reply;
>  	else
> diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
> index 81aca85..f40afb3 100644
> --- a/fs/lockd/svclock.c
> +++ b/fs/lockd/svclock.c
> @@ -460,8 +460,8 @@ out:
>   */
>  __be32
>  nlmsvc_testlock(struct svc_rqst *rqstp, struct nlm_file *file,
> -		struct nlm_lock *lock, struct nlm_lock *conflock,
> -		struct nlm_cookie *cookie)
> +		struct nlm_host *host, struct nlm_lock *lock,
> +		struct nlm_lock *conflock, struct nlm_cookie *cookie)
>  {
>  	struct nlm_block 	*block = NULL;
>  	int			error;
> @@ -479,16 +479,10 @@ nlmsvc_testlock(struct svc_rqst *rqstp, struct nlm_file *file,
>  
>  	if (block == NULL) {
>  		struct file_lock *conf = kzalloc(sizeof(*conf), GFP_KERNEL);
> -		struct nlm_host	*host;
>  
>  		if (conf == NULL)
>  			return nlm_granted;
> -		/* Create host handle for callback */
> -		host = nlmsvc_lookup_host(rqstp, lock->caller, lock->len);
> -		if (host == NULL) {
> -			kfree(conf);
> -			return nlm_lck_denied_nolocks;
> -		}
> +		nlm_get_host(host);
>  		block = nlmsvc_create_block(rqstp, host, file, lock, cookie);
>  		if (block == NULL) {
>  			kfree(conf);

By the way, it'd seem clearer if nlmsvc_create_block() did the job of
taking whatever reference it needed on "host" itself.

Seems like you could do the same for nlm_alloc_host() as well.

--b.

commit cc8c1b0a6514c670b1ab568241210bbdbece7923
Author: J. Bruce Fields <bfields@citi.umich.edu>
Date:   Tue Jul 15 15:05:45 2008 -0400

    lockd: get host reference in nlmsvc_create_block() instead of callers
    
    As it is it looks like there's an obvious reference count leak until you
    track down the definition of nlm_alloc_host() and see that it's
    guaranteed to consume a reference, success or failure.
    
    Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index 92c49d7..80d4f2e 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -180,6 +180,7 @@ nlmsvc_create_block(struct svc_rqst *rqstp, struct nlm_host *host,
 	struct nlm_block	*block;
 	struct nlm_rqst		*call = NULL;
 
+	nlm_get_host(host);
 	call = nlm_alloc_call(host);
 	if (call == NULL)
 		return NULL;
@@ -380,8 +381,7 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
 	 */
 	block = nlmsvc_lookup_block(file, lock);
 	if (block == NULL) {
-		block = nlmsvc_create_block(rqstp, nlm_get_host(host), file,
-					    lock, cookie);
+		block = nlmsvc_create_block(rqstp, host, file, lock, cookie);
 		ret = nlm_lck_denied_nolocks;
 		if (block == NULL)
 			goto out;
@@ -476,7 +476,6 @@ nlmsvc_testlock(struct svc_rqst *rqstp, struct nlm_file *file,
 
 		if (conf == NULL)
 			return nlm_granted;
-		nlm_get_host(host);
 		block = nlmsvc_create_block(rqstp, host, file, lock, cookie);
 		if (block == NULL) {
 			kfree(conf);