From e636825346b36a07ccfc8e30946d52855e21f681 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Mon, 19 Mar 2012 17:03:22 +0100
Subject: exit_signal: simplify the "we have changed execution domain" logic

exit_notify() checks "tsk->self_exec_id != tsk->parent_exec_id"
to handle the "we have changed execution domain" case.

We can change do_thread() to always set ->exit_signal = SIGCHLD
and remove this check to simplify the code.

We could change setup_new_exec() instead, this looks more logical
because it increments ->self_exec_id. But note that de_thread()
already resets ->exit_signal if it changes the leader, let's keep
both changes close to each other.

Note that we change ->exit_signal lockless, this changes the rules.
Thereafter ->exit_signal is not stable under tasklist but this is
fine, the only possible change is OLDSIG -> SIGCHLD. This can race
with eligible_child() but the race is harmless. We can race with
reparent_leader() which changes our ->exit_signal in parallel, but
it does the same change to SIGCHLD.

The noticeable user-visible change is that the execing task is not
"visible" to do_wait()->eligible_child(__WCLONE) right after exec.
To me this looks more logical, and this is consistent with mt case.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 fs/exec.c | 3 +++
 1 file changed, 3 insertions(+)

(limited to 'fs')

diff --git a/fs/exec.c b/fs/exec.c
index b0695a9900ef..1e94d2263ae0 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -977,6 +977,9 @@ static int de_thread(struct task_struct *tsk)
 	sig->notify_count = 0;
 
 no_thread_group:
+	/* we have changed execution domain */
+	tsk->exit_signal = SIGCHLD;
+
 	if (current->mm)
 		setmax_mm_hiwater_rss(&sig->maxrss, current->mm);
 
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