[01/15] SUNRPC: Remove the server 'authtab_lock' and just use RCU
diff mbox series

Message ID 20181001144157.3515-2-trond.myklebust@hammerspace.com
State New
Headers show
Series
  • Performance improvements for knfsd
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Commit Message

Trond Myklebust Oct. 1, 2018, 2:41 p.m. UTC
Module removal is RCU safe by design, so we really have no need to
lock the 'authtab[]' array.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 net/sunrpc/svcauth.c | 52 +++++++++++++++++++++++++++++---------------
 1 file changed, 34 insertions(+), 18 deletions(-)

Comments

J. Bruce Fields Oct. 2, 2018, 7:39 p.m. UTC | #1
On Mon, Oct 01, 2018 at 10:41:43AM -0400, Trond Myklebust wrote:
> Module removal is RCU safe by design, so we really have no need to
> lock the 'authtab[]' array.
> 
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
>  net/sunrpc/svcauth.c | 52 +++++++++++++++++++++++++++++---------------
>  1 file changed, 34 insertions(+), 18 deletions(-)
> 
> diff --git a/net/sunrpc/svcauth.c b/net/sunrpc/svcauth.c
> index bb8db3cb8032..f83443856cd1 100644
> --- a/net/sunrpc/svcauth.c
> +++ b/net/sunrpc/svcauth.c
> @@ -27,12 +27,32 @@
>  extern struct auth_ops svcauth_null;
>  extern struct auth_ops svcauth_unix;
>  
> -static DEFINE_SPINLOCK(authtab_lock);
> -static struct auth_ops	*authtab[RPC_AUTH_MAXFLAVOR] = {
> -	[0] = &svcauth_null,
> -	[1] = &svcauth_unix,
> +static struct auth_ops __rcu *authtab[RPC_AUTH_MAXFLAVOR] = {
> +	[RPC_AUTH_NULL] = (struct auth_ops __force __rcu *)&svcauth_null,
> +	[RPC_AUTH_UNIX] = (struct auth_ops __force __rcu *)&svcauth_unix,

I didn't know about "__rcu" and "__force __rcu".  Grepping turns up
relevant documentation for RCU_INIT_POINTER in include/linux/rcupdate.h,
OK, I think I get it.--b.

>  };
>  
> +static struct auth_ops *
> +svc_get_auth_ops(rpc_authflavor_t flavor)
> +{
> +	struct auth_ops		*aops;
> +
> +	if (flavor >= RPC_AUTH_MAXFLAVOR)
> +		return NULL;
> +	rcu_read_lock();
> +	aops = rcu_dereference(authtab[flavor]);
> +	if (aops != NULL && !try_module_get(aops->owner))
> +		aops = NULL;
> +	rcu_read_unlock();
> +	return aops;
> +}
> +
> +static void
> +svc_put_auth_ops(struct auth_ops *aops)
> +{
> +	module_put(aops->owner);
> +}
> +
>  int
>  svc_authenticate(struct svc_rqst *rqstp, __be32 *authp)
>  {
> @@ -45,14 +65,11 @@ svc_authenticate(struct svc_rqst *rqstp, __be32 *authp)
>  
>  	dprintk("svc: svc_authenticate (%d)\n", flavor);
>  
> -	spin_lock(&authtab_lock);
> -	if (flavor >= RPC_AUTH_MAXFLAVOR || !(aops = authtab[flavor]) ||
> -	    !try_module_get(aops->owner)) {
> -		spin_unlock(&authtab_lock);
> +	aops = svc_get_auth_ops(flavor);
> +	if (aops == NULL) {
>  		*authp = rpc_autherr_badcred;
>  		return SVC_DENIED;
>  	}
> -	spin_unlock(&authtab_lock);
>  
>  	rqstp->rq_auth_slack = 0;
>  	init_svc_cred(&rqstp->rq_cred);
> @@ -82,7 +99,7 @@ int svc_authorise(struct svc_rqst *rqstp)
>  
>  	if (aops) {
>  		rv = aops->release(rqstp);
> -		module_put(aops->owner);
> +		svc_put_auth_ops(aops);
>  	}
>  	return rv;
>  }
> @@ -90,13 +107,14 @@ int svc_authorise(struct svc_rqst *rqstp)
>  int
>  svc_auth_register(rpc_authflavor_t flavor, struct auth_ops *aops)
>  {
> +	struct auth_ops *old;
>  	int rv = -EINVAL;
> -	spin_lock(&authtab_lock);
> -	if (flavor < RPC_AUTH_MAXFLAVOR && authtab[flavor] == NULL) {
> -		authtab[flavor] = aops;
> -		rv = 0;
> +
> +	if (flavor < RPC_AUTH_MAXFLAVOR) {
> +		old = cmpxchg((struct auth_ops ** __force)&authtab[flavor], NULL, aops);
> +		if (old == NULL || old == aops)
> +			rv = 0;
>  	}
> -	spin_unlock(&authtab_lock);
>  	return rv;
>  }
>  EXPORT_SYMBOL_GPL(svc_auth_register);
> @@ -104,10 +122,8 @@ EXPORT_SYMBOL_GPL(svc_auth_register);
>  void
>  svc_auth_unregister(rpc_authflavor_t flavor)
>  {
> -	spin_lock(&authtab_lock);
>  	if (flavor < RPC_AUTH_MAXFLAVOR)
> -		authtab[flavor] = NULL;
> -	spin_unlock(&authtab_lock);
> +		rcu_assign_pointer(authtab[flavor], NULL);
>  }
>  EXPORT_SYMBOL_GPL(svc_auth_unregister);
>  
> -- 
> 2.17.1

Patch
diff mbox series

diff --git a/net/sunrpc/svcauth.c b/net/sunrpc/svcauth.c
index bb8db3cb8032..f83443856cd1 100644
--- a/net/sunrpc/svcauth.c
+++ b/net/sunrpc/svcauth.c
@@ -27,12 +27,32 @@ 
 extern struct auth_ops svcauth_null;
 extern struct auth_ops svcauth_unix;
 
-static DEFINE_SPINLOCK(authtab_lock);
-static struct auth_ops	*authtab[RPC_AUTH_MAXFLAVOR] = {
-	[0] = &svcauth_null,
-	[1] = &svcauth_unix,
+static struct auth_ops __rcu *authtab[RPC_AUTH_MAXFLAVOR] = {
+	[RPC_AUTH_NULL] = (struct auth_ops __force __rcu *)&svcauth_null,
+	[RPC_AUTH_UNIX] = (struct auth_ops __force __rcu *)&svcauth_unix,
 };
 
+static struct auth_ops *
+svc_get_auth_ops(rpc_authflavor_t flavor)
+{
+	struct auth_ops		*aops;
+
+	if (flavor >= RPC_AUTH_MAXFLAVOR)
+		return NULL;
+	rcu_read_lock();
+	aops = rcu_dereference(authtab[flavor]);
+	if (aops != NULL && !try_module_get(aops->owner))
+		aops = NULL;
+	rcu_read_unlock();
+	return aops;
+}
+
+static void
+svc_put_auth_ops(struct auth_ops *aops)
+{
+	module_put(aops->owner);
+}
+
 int
 svc_authenticate(struct svc_rqst *rqstp, __be32 *authp)
 {
@@ -45,14 +65,11 @@  svc_authenticate(struct svc_rqst *rqstp, __be32 *authp)
 
 	dprintk("svc: svc_authenticate (%d)\n", flavor);
 
-	spin_lock(&authtab_lock);
-	if (flavor >= RPC_AUTH_MAXFLAVOR || !(aops = authtab[flavor]) ||
-	    !try_module_get(aops->owner)) {
-		spin_unlock(&authtab_lock);
+	aops = svc_get_auth_ops(flavor);
+	if (aops == NULL) {
 		*authp = rpc_autherr_badcred;
 		return SVC_DENIED;
 	}
-	spin_unlock(&authtab_lock);
 
 	rqstp->rq_auth_slack = 0;
 	init_svc_cred(&rqstp->rq_cred);
@@ -82,7 +99,7 @@  int svc_authorise(struct svc_rqst *rqstp)
 
 	if (aops) {
 		rv = aops->release(rqstp);
-		module_put(aops->owner);
+		svc_put_auth_ops(aops);
 	}
 	return rv;
 }
@@ -90,13 +107,14 @@  int svc_authorise(struct svc_rqst *rqstp)
 int
 svc_auth_register(rpc_authflavor_t flavor, struct auth_ops *aops)
 {
+	struct auth_ops *old;
 	int rv = -EINVAL;
-	spin_lock(&authtab_lock);
-	if (flavor < RPC_AUTH_MAXFLAVOR && authtab[flavor] == NULL) {
-		authtab[flavor] = aops;
-		rv = 0;
+
+	if (flavor < RPC_AUTH_MAXFLAVOR) {
+		old = cmpxchg((struct auth_ops ** __force)&authtab[flavor], NULL, aops);
+		if (old == NULL || old == aops)
+			rv = 0;
 	}
-	spin_unlock(&authtab_lock);
 	return rv;
 }
 EXPORT_SYMBOL_GPL(svc_auth_register);
@@ -104,10 +122,8 @@  EXPORT_SYMBOL_GPL(svc_auth_register);
 void
 svc_auth_unregister(rpc_authflavor_t flavor)
 {
-	spin_lock(&authtab_lock);
 	if (flavor < RPC_AUTH_MAXFLAVOR)
-		authtab[flavor] = NULL;
-	spin_unlock(&authtab_lock);
+		rcu_assign_pointer(authtab[flavor], NULL);
 }
 EXPORT_SYMBOL_GPL(svc_auth_unregister);