[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>

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)) {