[PATCH] add child reaper to pid_namespace

Add a per pid_namespace child-reaper.  This is needed so processes are reaped
within the same pid space and do not spill over to the parent pid space.  Its
also needed so containers preserve existing semantic that pid == 1 would reap
orphaned children.

This is based on Eric Biederman's patch: http://lkml.org/lkml/2006/2/6/285

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Cc: Kirill Korotaev <dev@openvz.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 26 insertions, 11 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 28d9feedfd2..fd0e067952a 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -22,6 +22,7 @@
 #include <linux/file.h>
 #include <linux/binfmts.h>
 #include <linux/nsproxy.h>
+#include <linux/pid_namespace.h>
 #include <linux/ptrace.h>
 #include <linux/profile.h>
 #include <linux/mount.h>
@@ -48,7 +49,6 @@
 #include <asm/mmu_context.h>
 
 extern void sem_exit (void);
-extern struct task_struct *child_reaper;
 
 static void exit_mm(struct task_struct * tsk);
 
@@ -260,7 +260,8 @@ static int has_stopped_jobs(int pgrp)
 }
 
 /**
- * reparent_to_init - Reparent the calling kernel thread to the init task.
+ * reparent_to_init - Reparent the calling kernel thread to the init task
+ * of the pid space that the thread belongs to.
  *
  * If a kernel thread is launched as a result of a system call, or if
  * it ever exits, it should generally reparent itself to init so that
@@ -278,8 +279,8 @@ static void reparent_to_init(void)
 	ptrace_unlink(current);
 	/* Reparent to init */
 	remove_parent(current);
-	current->parent = child_reaper;
-	current->real_parent = child_reaper;
+	current->parent = child_reaper(current);
+	current->real_parent = child_reaper(current);
 	add_parent(current);
 
 	/* Set the exit signal to SIGCHLD so we signal init on exit */
@@ -662,7 +663,8 @@ reparent_thread(struct task_struct *p, struct task_struct *father, int traced)
  * When we die, we re-parent all our children.
  * Try to give them to another thread in our thread
  * group, and if no such member exists, give it to
- * the global child reaper process (ie "init")
+ * the child reaper process (ie "init") in our pid
+ * space.
  */
 static void
 forget_original_parent(struct task_struct *father, struct list_head *to_release)
@@ -673,7 +675,7 @@ forget_original_parent(struct task_struct *father, struct list_head *to_release)
 	do {
 		reaper = next_thread(reaper);
 		if (reaper == father) {
-			reaper = child_reaper;
+			reaper = child_reaper(father);
 			break;
 		}
 	} while (reaper->exit_state);
@@ -859,8 +861,13 @@ fastcall NORET_TYPE void do_exit(long code)
 		panic("Aiee, killing interrupt handler!");
 	if (unlikely(!tsk->pid))
 		panic("Attempted to kill the idle task!");
-	if (unlikely(tsk == child_reaper))
-		panic("Attempted to kill init!");
+	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;
+		else
+			panic("Attempted to kill init!");
+	}
+
 
 	if (unlikely(current->ptrace & PT_TRACE_EXIT)) {
 		current->ptrace_message = code;
diff --git a/kernel/pid.c b/kernel/pid.c
index 1d9cc268b49..2efe9d8d367 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -65,7 +65,8 @@ struct pid_namespace init_pid_ns = {
 	.pidmap = {
 		[ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL }
 	},
-	.last_pid = 0
+	.last_pid = 0,
+	.child_reaper = &init_task
 };
 
 /*
diff --git a/kernel/signal.c b/kernel/signal.c
index 9eac4db60ed..1921ffdc5e7 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -24,6 +24,9 @@
 #include <linux/signal.h>
 #include <linux/capability.h>
 #include <linux/freezer.h>
+#include <linux/pid_namespace.h>
+#include <linux/nsproxy.h>
+
 #include <asm/param.h>
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
@@ -1877,8 +1880,12 @@ relock:
 		if (sig_kernel_ignore(signr)) /* Default is nothing. */
 			continue;
 
-		/* Init gets no signals it doesn't want.  */
-		if (current == child_reaper)
+		/*
+		 * Init of a pid space gets no signals it doesn't want from
+		 * within that pid space. It can of course get signals from
+		 * its parent pid space.
+		 */
+		if (current == child_reaper(current))
 			continue;
 
 		if (sig_kernel_stop(signr)) {