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Subject[PATCH 5/6] 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>
---
kernel/exit.c | 56 +++++++++++++++++++++++++++++++++++---------------------
1 files changed, 35 insertions(+), 21 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 266e4f4..00c6139 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;
--
1.5.5.1


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