[RFC][PATCH 3/6] pid namespace : use struct pid_nr

[sukadev at us.ibm.com]

From: Cedric Le Goater <clg at fr.ibm.com>
Subject: [RFC][PATCH 3/6] pid namespace : use struct pid_nr

Allocate and attach a struct pid nr to the struct pid. When freeing the
pid, free the attached struct pid nrs.

Changelog:
	- [Serge Hallyn's comment]: Add comments on what pid->lock protects
	  and that pid->nr will eventually go away.

Signed-off-by: Cedric Le Goater <clg at fr.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>

---
 include/linux/pid.h |    3 +++
 kernel/pid.c        |   44 +++++++++++++++++++++++++++++++++++---------
 2 files changed, 38 insertions(+), 9 deletions(-)

Index: lx26-20-mm2b/include/linux/pid.h
===================================================================
--- lx26-20-mm2b.orig/include/linux/pid.h	2007-03-09 15:29:21.000000000 -0800
+++ lx26-20-mm2b/include/linux/pid.h	2007-03-09 15:49:29.000000000 -0800
@@ -66,6 +66,9 @@ struct pid
 	/* lists of tasks that use this pid */
 	struct hlist_head tasks[PIDTYPE_MAX];
 	struct rcu_head rcu;
+	struct hlist_head pid_nrs;
+	spinlock_t lock;
+	/* protects pid_nrs list */
 };
 
 extern struct pid init_struct_pid;
Index: lx26-20-mm2b/kernel/pid.c
===================================================================
--- lx26-20-mm2b.orig/kernel/pid.c	2007-03-09 15:29:21.000000000 -0800
+++ lx26-20-mm2b/kernel/pid.c	2007-03-09 15:29:23.000000000 -0800
@@ -180,8 +180,19 @@ fastcall void put_pid(struct pid *pid)
 	if (!pid)
 		return;
 	if ((atomic_read(&pid->count) == 1) ||
-	     atomic_dec_and_test(&pid->count))
+	     atomic_dec_and_test(&pid->count)) {
+		struct pid_nr* pid_nr;
+		struct hlist_node *pos, *next;
+
+		/*
+		 * rcu is not needed anymore
+		 */
+		hlist_for_each_entry_safe(pid_nr, pos, next, &pid->pid_nrs, node) {
+			hlist_del_init(&pid_nr->node);
+			free_pid_nr(pid_nr);
+		}
 		kmem_cache_free(pid_cachep, pid);
+	}
 }
 EXPORT_SYMBOL_GPL(put_pid);
 
@@ -202,6 +213,9 @@ void free_pid_nr(struct pid_nr *pid_nr)
 
 fastcall void free_pid(struct pid *pid)
 {
+	struct pid_nr* pid_nr;
+	struct hlist_node *pos;
+
 	/* We can be called with write_lock_irq(&tasklist_lock) held */
 	unsigned long flags;
 
@@ -209,7 +223,8 @@ fastcall void free_pid(struct pid *pid)
 	hlist_del_rcu(&pid->pid_chain);
 	spin_unlock_irqrestore(&pidmap_lock, flags);
 
-	free_pidmap(&init_pid_ns, pid->nr);
+	hlist_for_each_entry(pid_nr, pos, &pid->pid_nrs, node)
+		free_pidmap(pid_nr->pid_ns, pid_nr->nr);
 	call_rcu(&pid->rcu, delayed_put_pid);
 }
 
@@ -290,31 +305,42 @@ struct pid *alloc_pid(void)
 	struct pid *pid;
 	enum pid_type type;
 	int nr = -1;
+	struct pid_nr *pid_nr;
 
 	pid = kmem_cache_alloc(pid_cachep, GFP_KERNEL);
 	if (!pid)
-		goto out;
+		return NULL;
 
 	nr = alloc_pidmap(task_pid_ns(current));
 	if (nr < 0)
-		goto out_free;
+		goto out_free_pid;
+
+	pid_nr = alloc_pid_nr(task_pid_ns(current));
+	if (!pid_nr)
+		goto out_free_pidmap;
 
 	atomic_set(&pid->count, 1);
-	pid->nr = nr;
+	pid->nr = pid_nr->nr = nr; 	/* pid->nr to be removed soon */
 	for (type = 0; type < PIDTYPE_MAX; ++type)
 		INIT_HLIST_HEAD(&pid->tasks[type]);
 
+	spin_lock_init(&pid->lock);
+
+	INIT_HLIST_HEAD(&pid->pid_nrs);
+	hlist_add_head_rcu(&pid_nr->node, &pid->pid_nrs);
+
 	spin_lock_irq(&pidmap_lock);
 	hlist_add_head_rcu(&pid->pid_chain, &pid_hash[pid_hashfn(pid->nr)]);
 	spin_unlock_irq(&pidmap_lock);
 
-out:
 	return pid;
 
-out_free:
+out_free_pidmap:
+	free_pidmap(task_pid_ns(current), nr);
+
+out_free_pid:
 	kmem_cache_free(pid_cachep, pid);
-	pid = NULL;
-	goto out;
+	return NULL;
 }
 
 struct pid * fastcall find_pid(int nr)