pid namespaces: destroy pid namespace on init's death

Terminate all processes in a namespace when the reaper of the namespace is
exiting.  We do this by walking the pidmap of the namespace and sending
SIGKILL to all processes.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/kernel/pid.c b/kernel/pid.c
index d88b83eb703e..b3e6d7c41b97 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -34,6 +34,7 @@
 #include <linux/hash.h>
 #include <linux/pid_namespace.h>
 #include <linux/init_task.h>
+#include <linux/syscalls.h>
 
 #define pid_hashfn(nr, ns)      \
         hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
@@ -567,6 +568,43 @@ void free_pid_ns(struct kref *kref)
                 put_pid_ns(parent);
 }
 
+void zap_pid_ns_processes(struct pid_namespace *pid_ns)
+{
+        int nr;
+        int rc;
+
+        /*
+         * The last thread in the cgroup-init thread group is terminating.
+         * Find remaining pid_ts in the namespace, signal and wait for them
+         * to exit.
+         *
+         * Note:  This signals each threads in the namespace - even those that
+         *        belong to the same thread group, To avoid this, we would have
+         *        to walk the entire tasklist looking a processes in this
+         *        namespace, but that could be unnecessarily expensive if the
+         *        pid namespace has just a few processes. Or we need to
+         *        maintain a tasklist for each pid namespace.
+         *
+         */
+        read_lock(&tasklist_lock);
+        nr = next_pidmap(pid_ns, 1);
+        while (nr > 0) {
+                kill_proc_info(SIGKILL, SEND_SIG_PRIV, nr);
+                nr = next_pidmap(pid_ns, nr);
+        }
+        read_unlock(&tasklist_lock);
+
+        do {
+                clear_thread_flag(TIF_SIGPENDING);
+                rc = sys_wait4(-1, NULL, __WALL, NULL);
+        } while (rc != -ECHILD);
+
+
+        /* Child reaper for the pid namespace is going away */
+        pid_ns->child_reaper = NULL;
+        return;
+}
+
 /*
  * The pid hash table is scaled according to the amount of memory in the
  * machine.  From a minimum of 16 slots up to 4096 slots at one gigabyte or