[PATCH] making namespace_sem global

This removes the per-namespace semaphore in favor of a global semaphore.
This can have an effect on namespace scalability.

Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 23 insertions, 24 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 65f9c0ecc21c..4abee9ab009f 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -46,6 +46,7 @@ static int event;
 static struct list_head *mount_hashtable;
 static int hash_mask __read_mostly, hash_bits __read_mostly;
 static kmem_cache_t *mnt_cache;
+static struct rw_semaphore namespace_sem;
 
 static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
 {
@@ -250,7 +251,7 @@ static void *m_start(struct seq_file *m, loff_t *pos)
         struct list_head *p;
         loff_t l = *pos;
 
-        down_read(&n->sem);
+        down_read(&namespace_sem);
         list_for_each(p, &n->list)
                 if (!l--)
                         return list_entry(p, struct vfsmount, mnt_list);
@@ -267,8 +268,7 @@ static void *m_next(struct seq_file *m, void *v, loff_t *pos)
 
 static void m_stop(struct seq_file *m, void *v)
 {
-        struct namespace *n = m->private;
-        up_read(&n->sem);
+        up_read(&namespace_sem);
 }
 
 static inline void mangle(struct seq_file *m, const char *s)
@@ -487,7 +487,7 @@ static int do_umount(struct vfsmount *mnt, int flags)
                 return retval;
         }
 
-        down_write(&current->namespace->sem);
+        down_write(&namespace_sem);
         spin_lock(&vfsmount_lock);
         event++;
 
@@ -500,7 +500,7 @@ static int do_umount(struct vfsmount *mnt, int flags)
         spin_unlock(&vfsmount_lock);
         if (retval)
                 security_sb_umount_busy(mnt);
-        up_write(&current->namespace->sem);
+        up_write(&namespace_sem);
         release_mounts(&umount_list);
         return retval;
 }
@@ -678,7 +678,7 @@ static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
         if (err)
                 return err;
 
-        down_write(&current->namespace->sem);
+        down_write(&namespace_sem);
         err = -EINVAL;
         if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
                 goto out;
@@ -702,7 +702,7 @@ static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
         }
 
 out:
-        up_write(&current->namespace->sem);
+        up_write(&namespace_sem);
         path_release(&old_nd);
         return err;
 }
@@ -750,7 +750,7 @@ static int do_move_mount(struct nameidata *nd, char *old_name)
         if (err)
                 return err;
 
-        down_write(&current->namespace->sem);
+        down_write(&namespace_sem);
         while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
                 ;
         err = -EINVAL;
@@ -795,7 +795,7 @@ out2:
 out1:
         up(&nd->dentry->d_inode->i_sem);
 out:
-        up_write(&current->namespace->sem);
+        up_write(&namespace_sem);
         if (!err)
                 path_release(&parent_nd);
         path_release(&old_nd);
@@ -834,7 +834,7 @@ int do_add_mount(struct vfsmount *newmnt, struct nameidata *nd,
 {
         int err;
 
-        down_write(&current->namespace->sem);
+        down_write(&namespace_sem);
         /* Something was mounted here while we slept */
         while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
                 ;
@@ -862,11 +862,11 @@ int do_add_mount(struct vfsmount *newmnt, struct nameidata *nd,
                 list_add_tail(&newmnt->mnt_expire, fslist);
                 spin_unlock(&vfsmount_lock);
         }
-        up_write(&current->namespace->sem);
+        up_write(&namespace_sem);
         return 0;
 
 unlock:
-        up_write(&current->namespace->sem);
+        up_write(&namespace_sem);
         mntput(newmnt);
         return err;
 }
@@ -958,9 +958,9 @@ void mark_mounts_for_expiry(struct list_head *mounts)
                 get_namespace(namespace);
 
                 spin_unlock(&vfsmount_lock);
-                down_write(&namespace->sem);
+                down_write(&namespace_sem);
                 expire_mount(mnt, mounts, &umounts);
-                up_write(&namespace->sem);
+                up_write(&namespace_sem);
                 release_mounts(&umounts);
                 mntput(mnt);
                 put_namespace(namespace);
@@ -1127,17 +1127,16 @@ int copy_namespace(int flags, struct task_struct *tsk)
                 goto out;
 
         atomic_set(&new_ns->count, 1);
-        init_rwsem(&new_ns->sem);
         INIT_LIST_HEAD(&new_ns->list);
         init_waitqueue_head(&new_ns->poll);
         new_ns->event = 0;
 
-        down_write(&tsk->namespace->sem);
+        down_write(&namespace_sem);
         /* First pass: copy the tree topology */
         new_ns->root = copy_tree(namespace->root, namespace->root->mnt_root,
                                         CL_EXPIRE);
         if (!new_ns->root) {
-                up_write(&tsk->namespace->sem);
+                up_write(&namespace_sem);
                 kfree(new_ns);
                 goto out;
         }
@@ -1171,7 +1170,7 @@ int copy_namespace(int flags, struct task_struct *tsk)
                 p = next_mnt(p, namespace->root);
                 q = next_mnt(q, new_ns->root);
         }
-        up_write(&tsk->namespace->sem);
+        up_write(&namespace_sem);
 
         tsk->namespace = new_ns;
 
@@ -1356,7 +1355,7 @@ asmlinkage long sys_pivot_root(const char __user * new_root,
         user_nd.mnt = mntget(current->fs->rootmnt);
         user_nd.dentry = dget(current->fs->root);
         read_unlock(&current->fs->lock);
-        down_write(&current->namespace->sem);
+        down_write(&namespace_sem);
         down(&old_nd.dentry->d_inode->i_sem);
         error = -EINVAL;
         if (!check_mnt(user_nd.mnt))
@@ -1407,7 +1406,7 @@ asmlinkage long sys_pivot_root(const char __user * new_root,
         path_release(&parent_nd);
 out2:
         up(&old_nd.dentry->d_inode->i_sem);
-        up_write(&current->namespace->sem);
+        up_write(&namespace_sem);
         path_release(&user_nd);
         path_release(&old_nd);
 out1:
@@ -1434,7 +1433,6 @@ static void __init init_mount_tree(void)
                 panic("Can't allocate initial namespace");
         atomic_set(&namespace->count, 1);
         INIT_LIST_HEAD(&namespace->list);
-        init_rwsem(&namespace->sem);
         init_waitqueue_head(&namespace->poll);
         namespace->event = 0;
         list_add(&mnt->mnt_list, &namespace->list);
@@ -1459,6 +1457,8 @@ void __init mnt_init(unsigned long mempages)
         unsigned int nr_hash;
         int i;
 
+        init_rwsem(&namespace_sem);
+
         mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),
                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL, NULL);
 
@@ -1507,11 +1507,11 @@ void __put_namespace(struct namespace *namespace)
         LIST_HEAD(umount_list);
         namespace->root = NULL;
         spin_unlock(&vfsmount_lock);
-        down_write(&namespace->sem);
+        down_write(&namespace_sem);
         spin_lock(&vfsmount_lock);
         umount_tree(root, &umount_list);
         spin_unlock(&vfsmount_lock);
-        up_write(&namespace->sem);
+        up_write(&namespace_sem);
         release_mounts(&umount_list);
         kfree(namespace);
 }
diff --git a/include/linux/namespace.h b/include/linux/namespace.h
index 6f0f25d64c38..6731977c4c13 100644
--- a/include/linux/namespace.h
+++ b/include/linux/namespace.h
@@ -9,7 +9,6 @@ struct namespace {
         atomic_t                count;
         struct vfsmount *       root;
         struct list_head        list;
-        struct rw_semaphore     sem;
         wait_queue_head_t poll;
         int event;
 };