exit: reparent: introduce find_child_reaper()

find_new_reaper() does 2 completely different things.  Not only it finds a
reaper, it also updates pid_ns->child_reaper or kills the whole namespace
if the caller is ->child_reaper.

Now that has_child_subreaper logic doesn't depend on child_reaper check we
can move that pid_ns code into a separate helper.  IMHO this makes the
code more clean, and this allows the next changes.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kay Sievers <kay@vrfy.org>
Cc: Lennart Poettering <lennart@poettering.net>
Cc: Sterling Alexander <stalexan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 35 insertions, 21 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 576949ce5665..930fbe1b5ee2 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -459,6 +459,34 @@ static void exit_mm(struct task_struct *tsk)
         clear_thread_flag(TIF_MEMDIE);
 }
 
+static struct task_struct *find_child_reaper(struct task_struct *father)
+        __releases(&tasklist_lock)
+        __acquires(&tasklist_lock)
+{
+        struct pid_namespace *pid_ns = task_active_pid_ns(father);
+        struct task_struct *reaper = pid_ns->child_reaper;
+
+        if (likely(reaper != father))
+                return reaper;
+
+        for_each_thread(father, reaper) {
+                if (reaper->flags & PF_EXITING)
+                        continue;
+                pid_ns->child_reaper = reaper;
+                return reaper;
+        }
+
+        write_unlock_irq(&tasklist_lock);
+        if (unlikely(pid_ns == &init_pid_ns)) {
+                panic("Attempted to kill init! exitcode=0x%08x\n",
+                        father->signal->group_exit_code ?: father->exit_code);
+        }
+        zap_pid_ns_processes(pid_ns);
+        write_lock_irq(&tasklist_lock);
+
+        return father;
+}
+
 /*
  * When we die, we re-parent all our children, and try to:
  * 1. give them to another thread in our thread group, if such a member exists
@@ -466,33 +494,17 @@ static void exit_mm(struct task_struct *tsk)
  *    child_subreaper for its children (like a service manager)
  * 3. give it to the init process (PID 1) in our pid namespace
  */
-static struct task_struct *find_new_reaper(struct task_struct *father)
-        __releases(&tasklist_lock)
-        __acquires(&tasklist_lock)
+static struct task_struct *find_new_reaper(struct task_struct *father,
+                                           struct task_struct *child_reaper)
 {
-        struct pid_namespace *pid_ns = task_active_pid_ns(father);
         struct task_struct *thread;
 
         for_each_thread(father, thread) {
                 if (thread->flags & PF_EXITING)
                         continue;
-                if (unlikely(pid_ns->child_reaper == father))
-                        pid_ns->child_reaper = thread;
                 return thread;
         }
 
-        if (unlikely(pid_ns->child_reaper == father)) {
-                write_unlock_irq(&tasklist_lock);
-                if (unlikely(pid_ns == &init_pid_ns)) {
-                        panic("Attempted to kill init! exitcode=0x%08x\n",
-                                father->signal->group_exit_code ?:
-                                        father->exit_code);
-                }
-
-                zap_pid_ns_processes(pid_ns);
-                write_lock_irq(&tasklist_lock);
-        }
-
         if (father->signal->has_child_subreaper) {
                 struct task_struct *reaper;
                 /*
@@ -501,7 +513,7 @@ static struct task_struct *find_new_reaper(struct task_struct *father)
                  * namespace, this is safe because all its threads are dead.
                  */
                 for (reaper = father;
-                     !same_thread_group(reaper, pid_ns->child_reaper);
+                     !same_thread_group(reaper, child_reaper);
                      reaper = reaper->real_parent) {
                         /* call_usermodehelper() descendants need this check */
                         if (reaper == &init_task)
@@ -515,7 +527,7 @@ static struct task_struct *find_new_reaper(struct task_struct *father)
                 }
         }
 
-        return pid_ns->child_reaper;
+        return child_reaper;
 }
 
 /*
@@ -552,7 +564,9 @@ static void forget_original_parent(struct task_struct *father)
                 exit_ptrace(father, &dead_children);
 
         /* Can drop and reacquire tasklist_lock */
-        reaper = find_new_reaper(father);
+        reaper = find_child_reaper(father);
+
+        reaper = find_new_reaper(father, reaper);
         list_for_each_entry(p, &father->children, sibling) {
                 for_each_thread(p, t) {
                         t->real_parent = reaper;