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Subject[PATCH 16/26] exit: Fix reporting a ptraced !reparented leader has exited
When a task exits and uses do_notify_parent to send tsk->exit_signal
or SIGCHLD this has one of two possible meanings.
- The ptraced task has exited
- The thread group has exited

Linux resolves this ambiguity by preferring the thread group exit
interpretation if it is possible. As the exit of a thread group
containing a task is a superset of the exit of a task.

The code attempts to implement this in it's selection of signal
before calling do_notify_parent for a ptraced task. Unfortunately
it fails to properly handle the case when the thread_group is still
running (but it's leader has exited).

Fix this for a ptraced child leader by skipping the notification
instead of changing the exit signal. If we skip sending the signal in
exit_noitfy, when the last of the other threads are reaped
release_task will send the signal for us.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
kernel/exit.c | 15 +++++----------
1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 85b34eff8807..72591eb5e361 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -639,7 +639,7 @@ static void forget_original_parent(struct task_struct *father,
*/
static void exit_notify(struct task_struct *tsk, int group_dead)
{
- bool autoreap;
+ bool autoreap = true;
struct task_struct *p, *n;
LIST_HEAD(dead);

@@ -649,17 +649,12 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
if (group_dead)
kill_orphaned_pgrp(tsk->group_leader, NULL);

- if (unlikely(tsk->ptrace)) {
- int sig = thread_group_leader(tsk) &&
- thread_group_empty(tsk) &&
- !ptrace_reparented(tsk) ?
- tsk->exit_signal : SIGCHLD;
- autoreap = do_notify_parent(tsk, sig);
- } else if (thread_group_leader(tsk)) {
+ if (thread_group_leader(tsk) && !ptrace_reparented(tsk)) {
autoreap = thread_group_empty(tsk) &&
do_notify_parent(tsk, tsk->exit_signal);
- } else {
- autoreap = true;
+ }
+ else if (unlikely(tsk->ptrace)) {
+ autoreap = do_notify_parent(tsk, SIGCHLD);
}

tsk->exit_state = autoreap ? EXIT_DEAD : EXIT_ZOMBIE;
--
2.10.1
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