[Devel] [RFC][PATCH 06/14] Populate pid_nrs list with entry for init-pid-ns

[sukadev at us.ibm.com]

From: Cedric Le Goater <clg at fr.ibm.com>
Subject: [RFC][PATCH 06/14] Populate pid_nrs list with entry for init-pid-ns

Create/destroy the pid->pid_nrs list - when allocating/freeing  a struct pid.
The pid_nrs list contains just a single struct pid_nr for now, (corresponding
to init-pid-ns). 

To enable finding a process based on any of its pid_t values, replace the
use struct pid_nr, rather than struct pid, in the pid_hash table. 

Finally, reimplement find_pid() and pid_nr() based on the pid_nrs list.

Changelog:
	- [Serge Hallyn's comment]: Add comments on what pid->lock protects
	  and that pid->nr will eventually go away.
	- [Eric Biederman and containers list comments]: Reworked patches
	  to drop support for unsharing pid namespace and to replace
	  struct pid with struct pid_nr in the pid_hash table.

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 |    9 ------
 kernel/pid.c        |   73 ++++++++++++++++++++++++++++++++++------------------
 2 files changed, 50 insertions(+), 32 deletions(-)

Index: 2.6.21-rc3-mm2/kernel/pid.c
===================================================================
--- 2.6.21-rc3-mm2.orig/kernel/pid.c
+++ 2.6.21-rc3-mm2/kernel/pid.c
@@ -194,8 +194,15 @@ static void delayed_put_pid(struct rcu_h

 void free_pid_nr(struct pid_nr *pid_nr)
 {
+	/* We can be called with write_lock_irq(&tasklist_lock) held */
+	unsigned long flags;
+
 	free_pidmap(pid_nr->pid_ns, pid_nr->nr);

+	spin_lock_irqsave(&pidmap_lock, flags);
+	hlist_del_rcu(&pid_nr->pid_chain);
+	spin_unlock_irqrestore(&pidmap_lock, flags);
+
 	hlist_del_init(&pid_nr->node);

 	put_pid_ns(pid_nr->pid_ns);
@@ -204,14 +211,12 @@ void free_pid_nr(struct pid_nr *pid_nr)

 fastcall void free_pid(struct pid *pid)
 {
-	/* We can be called with write_lock_irq(&tasklist_lock) held */
-	unsigned long flags;
+	struct pid_nr *pid_nr;
+	struct hlist_node *pos, *next;

-	spin_lock_irqsave(&pidmap_lock, flags);
-	hlist_del_rcu(&pid->pid_chain);
-	spin_unlock_irqrestore(&pidmap_lock, flags);
+	hlist_for_each_entry_safe(pid_nr, pos, next, &pid->pid_nrs, node)
+		free_pid_nr(pid_nr);

-	free_pidmap(&init_pid_ns, pid->nr);
 	call_rcu(&pid->rcu, delayed_put_pid);
 }

@@ -242,50 +247,70 @@ struct pid_nr *alloc_pid_nr(struct pid_n
 	 */
 	pid_nr->pid = pid;

+	spin_lock_irq(&pidmap_lock);
+	hlist_add_head_rcu(&pid_nr->pid_chain, &pid_hash[pid_hashfn(nr)]);
+	spin_unlock_irq(&pidmap_lock);
+
 	return pid_nr;
 }

+pid_t pid_nr(struct pid *pid)
+{
+	struct pid_nr* pid_nr;
+	struct hlist_node *pos;
+	struct pid_namespace *ns = task_pid_ns(current);
+
+	if (!pid)
+		return 0;
+
+	hlist_for_each_entry(pid_nr, pos, &pid->pid_nrs, node)
+		if (pid_nr->pid_ns == ns)
+			return pid_nr->nr;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pid_nr);
+
 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;
-
-	nr = alloc_pidmap(task_pid_ns(current));
-	if (nr < 0)
-		goto out_free;
+		return NULL;

 	atomic_set(&pid->count, 1);
-	pid->nr = nr;
+
 	for (type = 0; type < PIDTYPE_MAX; ++type)
 		INIT_HLIST_HEAD(&pid->tasks[type]);

-	spin_lock_irq(&pidmap_lock);
-	hlist_add_head_rcu(&pid->pid_chain, &pid_hash[pid_hashfn(pid->nr)]);
-	spin_unlock_irq(&pidmap_lock);
+	INIT_HLIST_HEAD(&pid->pid_nrs);
+
+	pid_nr = alloc_pid_nr(task_pid_ns(current), pid);
+	if (!pid_nr)
+		goto out_free_pid;
+
+	pid->nr = pid_nr->nr; 		/* pid->nr to be removed soon */
+	hlist_add_head(&pid_nr->node, &pid->pid_nrs);

-out:
 	return pid;

-out_free:
+out_free_pid:
 	kmem_cache_free(pid_cachep, pid);
-	pid = NULL;
-	goto out;
+	return NULL;
 }

 struct pid * fastcall find_pid(int nr)
 {
 	struct hlist_node *elem;
-	struct pid *pid;
+	struct pid_nr *pid_nr;
+	struct pid_namespace *ns = task_pid_ns(current);

-	hlist_for_each_entry_rcu(pid, elem,
+	hlist_for_each_entry_rcu(pid_nr, elem,
 			&pid_hash[pid_hashfn(nr)], pid_chain) {
-		if (pid->nr == nr)
-			return pid;
+		if (pid_nr->nr == nr && pid_nr->pid_ns == ns)
+			return pid_nr->pid;
 	}
 	return NULL;
 }
Index: 2.6.21-rc3-mm2/include/linux/pid.h
===================================================================
--- 2.6.21-rc3-mm2.orig/include/linux/pid.h
+++ 2.6.21-rc3-mm2/include/linux/pid.h
@@ -120,14 +120,7 @@ extern struct pid_nr *alloc_pid_nr(struc
 			struct pid *pid);
 extern struct pid *alloc_pid(void);
 extern void FASTCALL(free_pid(struct pid *pid));
-
-static inline pid_t pid_nr(struct pid *pid)
-{
-	pid_t nr = 0;
-	if (pid)
-		nr = pid->nr;
-	return nr;
-}
+extern pid_t pid_nr(struct pid *pid);

 #define do_each_pid_task(pid, type, task)				\
 	do {								\

-- 

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