[Devel] [PATCH 1/6] Define and use task_active_pid_ns() wrapper

[sukadev at us.ibm.com]

Subject: [PATCH 1/6] Define and use task_active_pid_ns() wrapper

From: Sukadev Bhattiprolu <sukadev at us.ibm.com>

With multiple pid namespaces, a process is known by some pid_t in
every ancestor pid namespace.  Every time the process forks, the
child process also gets a pid_t in every ancestor pid namespace.

While a process is visible in >=1 pid namespaces, it can see pid_t's
in only one pid namespace.  We call this pid namespace it's "active
pid namespace", and it is always the youngest pid namespace in which
the process is known.

This patch defines and uses a wrapper to find the active pid namespace
of a process. The implementation of the wrapper will be changed in 
when support for multiple pid namespaces are added.

Changelog:
	2.6.22-rc4-mm2-pidns1:
	- [Pavel Emelianov, Alexey Dobriyan] Back out the change to use
	  task_active_pid_ns() in child_reaper() since task->nsproxy
	  can be NULL during task exit (so child_reaper() continues to
	  use init_pid_ns).

	  to implement child_reaper() since init_pid_ns.child_reaper to
	  implement child_reaper() since tsk->nsproxy can be NULL during exit.

	2.6.21-rc6-mm1:
	- Rename task_pid_ns() to task_active_pid_ns() to reflect that a
	  process can have multiple pid namespaces.

Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
---
 fs/exec.c                     |    2 +-
 fs/proc/proc_misc.c           |    3 ++-
 include/linux/pid_namespace.h |    5 +++++
 kernel/exit.c                 |    5 +++--
 kernel/nsproxy.c              |    2 +-
 kernel/pid.c                  |    4 ++--
 6 files changed, 14 insertions(+), 7 deletions(-)

Index: lx26-22-rc6-mm1/include/linux/pid_namespace.h
===================================================================
--- lx26-22-rc6-mm1.orig/include/linux/pid_namespace.h	2007-07-05 18:53:43.000000000 -0700
+++ lx26-22-rc6-mm1/include/linux/pid_namespace.h	2007-07-05 18:53:48.000000000 -0700
@@ -37,6 +37,11 @@ static inline void put_pid_ns(struct pid
 	kref_put(&ns->kref, free_pid_ns);
 }
 
+static inline struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
+{
+	return tsk->nsproxy->pid_ns;
+}
+
 static inline struct task_struct *child_reaper(struct task_struct *tsk)
 {
 	return init_pid_ns.child_reaper;
Index: lx26-22-rc6-mm1/fs/exec.c
===================================================================
--- lx26-22-rc6-mm1.orig/fs/exec.c	2007-07-05 18:53:43.000000000 -0700
+++ lx26-22-rc6-mm1/fs/exec.c	2007-07-05 18:53:48.000000000 -0700
@@ -827,7 +827,7 @@ static int de_thread(struct task_struct 
 	 * so it is safe to do it under read_lock.
 	 */
 	if (unlikely(tsk->group_leader == child_reaper(tsk)))
-		tsk->nsproxy->pid_ns->child_reaper = tsk;
+		task_active_pid_ns(tsk)->child_reaper = tsk;
 
 	zap_other_threads(tsk);
 	read_unlock(&tasklist_lock);
Index: lx26-22-rc6-mm1/fs/proc/proc_misc.c
===================================================================
--- lx26-22-rc6-mm1.orig/fs/proc/proc_misc.c	2007-07-05 18:53:43.000000000 -0700
+++ lx26-22-rc6-mm1/fs/proc/proc_misc.c	2007-07-05 18:53:48.000000000 -0700
@@ -94,7 +94,8 @@ static int loadavg_read_proc(char *page,
 		LOAD_INT(a), LOAD_FRAC(a),
 		LOAD_INT(b), LOAD_FRAC(b),
 		LOAD_INT(c), LOAD_FRAC(c),
-		nr_running(), nr_threads, current->nsproxy->pid_ns->last_pid);
+		nr_running(), nr_threads,
+		task_active_pid_ns(current)->last_pid);
 	return proc_calc_metrics(page, start, off, count, eof, len);
 }
 
Index: lx26-22-rc6-mm1/kernel/exit.c
===================================================================
--- lx26-22-rc6-mm1.orig/kernel/exit.c	2007-07-05 18:53:43.000000000 -0700
+++ lx26-22-rc6-mm1/kernel/exit.c	2007-07-05 18:53:48.000000000 -0700
@@ -909,8 +909,9 @@ fastcall NORET_TYPE void do_exit(long co
 	if (unlikely(!tsk->pid))
 		panic("Attempted to kill the idle task!");
 	if (unlikely(tsk == child_reaper(tsk))) {
-		if (tsk->nsproxy->pid_ns != &init_pid_ns)
-			tsk->nsproxy->pid_ns->child_reaper = init_pid_ns.child_reaper;
+		if (task_active_pid_ns(tsk) != &init_pid_ns)
+			task_active_pid_ns(tsk)->child_reaper =
+					init_pid_ns.child_reaper;
 		else
 			panic("Attempted to kill init!");
 	}
Index: lx26-22-rc6-mm1/kernel/pid.c
===================================================================
--- lx26-22-rc6-mm1.orig/kernel/pid.c	2007-07-05 18:53:43.000000000 -0700
+++ lx26-22-rc6-mm1/kernel/pid.c	2007-07-05 18:53:48.000000000 -0700
@@ -213,7 +213,7 @@ struct pid *alloc_pid(void)
 	if (!pid)
 		goto out;
 
-	nr = alloc_pidmap(current->nsproxy->pid_ns);
+	nr = alloc_pidmap(task_active_pid_ns(current));
 	if (nr < 0)
 		goto out_free;
 
@@ -358,7 +358,7 @@ struct pid *find_ge_pid(int nr)
 		pid = find_pid(nr);
 		if (pid)
 			break;
-		nr = next_pidmap(current->nsproxy->pid_ns, nr);
+		nr = next_pidmap(task_active_pid_ns(current), nr);
 	} while (nr > 0);
 
 	return pid;
Index: lx26-22-rc6-mm1/kernel/nsproxy.c
===================================================================
--- lx26-22-rc6-mm1.orig/kernel/nsproxy.c	2007-07-05 18:53:42.000000000 -0700
+++ lx26-22-rc6-mm1/kernel/nsproxy.c	2007-07-05 18:54:07.000000000 -0700
@@ -86,7 +86,7 @@ static struct nsproxy *create_new_namesp
 		goto out_ipc;
 	}
 
-	new_nsp->pid_ns = copy_pid_ns(flags, tsk->nsproxy->pid_ns);
+	new_nsp->pid_ns = copy_pid_ns(flags, task_active_pid_ns(tsk));
 	if (IS_ERR(new_nsp->pid_ns)) {
 		err = PTR_ERR(new_nsp->pid_ns);
 		goto out_pid;
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