From 4e4c3bef4471c8a06406abd2e3d9493e8478feff Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Thu, 27 Sep 2018 13:12:44 -0400 Subject: [PATCH] SUNRPC: Remove rpc_authflavor_lock in favour of RCU locking Module removal is RCU safe by design, so we really have no need to lock the auth_flavors[] array. Substitute a lockless scheme to add/remove entries in the array, and then use rcu. Signed-off-by: Trond Myklebust --- net/sunrpc/auth.c | 128 ++++++++++++++++++++++++++---------------------------- 1 file changed, 62 insertions(+), 66 deletions(-) diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c index 59df5cd..32985aa 100644 --- a/net/sunrpc/auth.c +++ b/net/sunrpc/auth.c @@ -30,10 +30,9 @@ struct rpc_cred_cache { static unsigned int auth_hashbits = RPC_CREDCACHE_DEFAULT_HASHBITS; -static DEFINE_SPINLOCK(rpc_authflavor_lock); -static const struct rpc_authops *auth_flavors[RPC_AUTH_MAXFLAVOR] = { - &authnull_ops, /* AUTH_NULL */ - &authunix_ops, /* AUTH_UNIX */ +static const struct rpc_authops __rcu *auth_flavors[RPC_AUTH_MAXFLAVOR] = { + [RPC_AUTH_NULL] = (const struct rpc_authops __force __rcu *)&authnull_ops, + [RPC_AUTH_UNIX] = (const struct rpc_authops __force __rcu *)&authunix_ops, NULL, /* others can be loadable modules */ }; @@ -93,39 +92,65 @@ pseudoflavor_to_flavor(u32 flavor) { int rpcauth_register(const struct rpc_authops *ops) { + const struct rpc_authops *old; rpc_authflavor_t flavor; - int ret = -EPERM; if ((flavor = ops->au_flavor) >= RPC_AUTH_MAXFLAVOR) return -EINVAL; - spin_lock(&rpc_authflavor_lock); - if (auth_flavors[flavor] == NULL) { - auth_flavors[flavor] = ops; - ret = 0; - } - spin_unlock(&rpc_authflavor_lock); - return ret; + old = cmpxchg((const struct rpc_authops ** __force)&auth_flavors[flavor], NULL, ops); + if (old == NULL || old == ops) + return 0; + return -EPERM; } EXPORT_SYMBOL_GPL(rpcauth_register); int rpcauth_unregister(const struct rpc_authops *ops) { + const struct rpc_authops *old; rpc_authflavor_t flavor; - int ret = -EPERM; if ((flavor = ops->au_flavor) >= RPC_AUTH_MAXFLAVOR) return -EINVAL; - spin_lock(&rpc_authflavor_lock); - if (auth_flavors[flavor] == ops) { - auth_flavors[flavor] = NULL; - ret = 0; - } - spin_unlock(&rpc_authflavor_lock); - return ret; + + old = cmpxchg((const struct rpc_authops ** __force)&auth_flavors[flavor], ops, NULL); + if (old == ops || old == NULL) + return 0; + return -EPERM; } EXPORT_SYMBOL_GPL(rpcauth_unregister); +static const struct rpc_authops * +rpcauth_get_authops(rpc_authflavor_t flavor) +{ + const struct rpc_authops *ops; + + if (flavor >= RPC_AUTH_MAXFLAVOR) + return NULL; + + rcu_read_lock(); + ops = rcu_dereference(auth_flavors[flavor]); + if (ops == NULL) { + rcu_read_unlock(); + request_module("rpc-auth-%u", flavor); + rcu_read_lock(); + ops = rcu_dereference(auth_flavors[flavor]); + if (ops == NULL) + goto out; + } + if (!try_module_get(ops->owner)) + ops = NULL; +out: + rcu_read_unlock(); + return ops; +} + +static void +rpcauth_put_authops(const struct rpc_authops *ops) +{ + module_put(ops->owner); +} + /** * rpcauth_get_pseudoflavor - check if security flavor is supported * @flavor: a security flavor @@ -138,25 +163,16 @@ EXPORT_SYMBOL_GPL(rpcauth_unregister); rpc_authflavor_t rpcauth_get_pseudoflavor(rpc_authflavor_t flavor, struct rpcsec_gss_info *info) { - const struct rpc_authops *ops; + const struct rpc_authops *ops = rpcauth_get_authops(flavor); rpc_authflavor_t pseudoflavor; - ops = auth_flavors[flavor]; - if (ops == NULL) - request_module("rpc-auth-%u", flavor); - spin_lock(&rpc_authflavor_lock); - ops = auth_flavors[flavor]; - if (ops == NULL || !try_module_get(ops->owner)) { - spin_unlock(&rpc_authflavor_lock); + if (!ops) return RPC_AUTH_MAXFLAVOR; - } - spin_unlock(&rpc_authflavor_lock); - pseudoflavor = flavor; if (ops->info2flavor != NULL) pseudoflavor = ops->info2flavor(info); - module_put(ops->owner); + rpcauth_put_authops(ops); return pseudoflavor; } EXPORT_SYMBOL_GPL(rpcauth_get_pseudoflavor); @@ -176,25 +192,15 @@ rpcauth_get_gssinfo(rpc_authflavor_t pseudoflavor, struct rpcsec_gss_info *info) const struct rpc_authops *ops; int result; - if (flavor >= RPC_AUTH_MAXFLAVOR) - return -EINVAL; - - ops = auth_flavors[flavor]; + ops = rpcauth_get_authops(flavor); if (ops == NULL) - request_module("rpc-auth-%u", flavor); - spin_lock(&rpc_authflavor_lock); - ops = auth_flavors[flavor]; - if (ops == NULL || !try_module_get(ops->owner)) { - spin_unlock(&rpc_authflavor_lock); return -ENOENT; - } - spin_unlock(&rpc_authflavor_lock); result = -ENOENT; if (ops->flavor2info != NULL) result = ops->flavor2info(pseudoflavor, info); - module_put(ops->owner); + rpcauth_put_authops(ops); return result; } EXPORT_SYMBOL_GPL(rpcauth_get_gssinfo); @@ -212,15 +218,13 @@ EXPORT_SYMBOL_GPL(rpcauth_get_gssinfo); int rpcauth_list_flavors(rpc_authflavor_t *array, int size) { - rpc_authflavor_t flavor; - int result = 0; + const struct rpc_authops *ops; + rpc_authflavor_t flavor, pseudos[4]; + int i, len, result = 0; - spin_lock(&rpc_authflavor_lock); + rcu_read_lock(); for (flavor = 0; flavor < RPC_AUTH_MAXFLAVOR; flavor++) { - const struct rpc_authops *ops = auth_flavors[flavor]; - rpc_authflavor_t pseudos[4]; - int i, len; - + ops = rcu_dereference(auth_flavors[flavor]); if (result >= size) { result = -ENOMEM; break; @@ -245,7 +249,7 @@ rpcauth_list_flavors(rpc_authflavor_t *array, int size) array[result++] = pseudos[i]; } } - spin_unlock(&rpc_authflavor_lock); + rcu_read_unlock(); dprintk("RPC: %s returns %d\n", __func__, result); return result; @@ -255,25 +259,17 @@ EXPORT_SYMBOL_GPL(rpcauth_list_flavors); struct rpc_auth * rpcauth_create(const struct rpc_auth_create_args *args, struct rpc_clnt *clnt) { - struct rpc_auth *auth; + struct rpc_auth *auth = ERR_PTR(-EINVAL); const struct rpc_authops *ops; - u32 flavor = pseudoflavor_to_flavor(args->pseudoflavor); + u32 flavor = pseudoflavor_to_flavor(args->pseudoflavor); - auth = ERR_PTR(-EINVAL); - if (flavor >= RPC_AUTH_MAXFLAVOR) + ops = rpcauth_get_authops(flavor); + if (ops == NULL) goto out; - if ((ops = auth_flavors[flavor]) == NULL) - request_module("rpc-auth-%u", flavor); - spin_lock(&rpc_authflavor_lock); - ops = auth_flavors[flavor]; - if (ops == NULL || !try_module_get(ops->owner)) { - spin_unlock(&rpc_authflavor_lock); - goto out; - } - spin_unlock(&rpc_authflavor_lock); auth = ops->create(args, clnt); - module_put(ops->owner); + + rpcauth_put_authops(ops); if (IS_ERR(auth)) return auth; if (clnt->cl_auth) -- 2.7.4