NFS: Clean up locking the nfs_versions list

This patch replaces the nfs_version_mutex and nfs_version_lock with a
single RW lock that protects access to the nfs_versions list.

The mutex around request_module() seemed unnecessary to me, and I
couldn't find any other callers using a lock around calls to
request_module() when I looked.

At the same time, I saw fs/filesystems.c using a RW lock to protect
their filesystems list. This seems like a better idea than a spinlock to
me, so I'm also making that change while I'm here.

Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 03ecc77..8bcc61a 100644 (file)
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -55,8 +55,7 @@
 #define NFSDBG_FACILITY                NFSDBG_CLIENT
 
 static DECLARE_WAIT_QUEUE_HEAD(nfs_client_active_wq);
-static DEFINE_SPINLOCK(nfs_version_lock);
-static DEFINE_MUTEX(nfs_version_mutex);
+static DEFINE_RWLOCK(nfs_version_lock);
 static LIST_HEAD(nfs_versions);
 
 /*
@@ -79,16 +78,16 @@ const struct rpc_program nfs_program = {
 static struct nfs_subversion *find_nfs_version(unsigned int version)
 {
        struct nfs_subversion *nfs;
-       spin_lock(&nfs_version_lock);
+       read_lock(&nfs_version_lock);
 
        list_for_each_entry(nfs, &nfs_versions, list) {
                if (nfs->rpc_ops->version == version) {
-                       spin_unlock(&nfs_version_lock);
+                       read_unlock(&nfs_version_lock);
                        return nfs;
                }
        }
 
-       spin_unlock(&nfs_version_lock);
+       read_unlock(&nfs_version_lock);
        return ERR_PTR(-EPROTONOSUPPORT);
 }
 
@@ -97,10 +96,8 @@ struct nfs_subversion *get_nfs_version(unsigned int version)
        struct nfs_subversion *nfs = find_nfs_version(version);
 
        if (IS_ERR(nfs)) {
-               mutex_lock(&nfs_version_mutex);
                request_module("nfsv%d", version);
                nfs = find_nfs_version(version);
-               mutex_unlock(&nfs_version_mutex);
        }
 
        if (!IS_ERR(nfs) && !try_module_get(nfs->owner))
@@ -115,23 +112,23 @@ void put_nfs_version(struct nfs_subversion *nfs)
 
 void register_nfs_version(struct nfs_subversion *nfs)
 {
-       spin_lock(&nfs_version_lock);
+       write_lock(&nfs_version_lock);
 
        list_add(&nfs->list, &nfs_versions);
        nfs_version[nfs->rpc_ops->version] = nfs->rpc_vers;
 
-       spin_unlock(&nfs_version_lock);
+       write_unlock(&nfs_version_lock);
 }
 EXPORT_SYMBOL_GPL(register_nfs_version);
 
 void unregister_nfs_version(struct nfs_subversion *nfs)
 {
-       spin_lock(&nfs_version_lock);
+       write_lock(&nfs_version_lock);
 
        nfs_version[nfs->rpc_ops->version] = NULL;
        list_del(&nfs->list);
 
-       spin_unlock(&nfs_version_lock);
+       write_unlock(&nfs_version_lock);
 }
 EXPORT_SYMBOL_GPL(unregister_nfs_version);