exit_signal: simplify the "we have changed execution domain" logic

commit e636825346b36a07ccfc8e30946d52855e21f681 upstream.

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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/exec.c b/fs/exec.c
index 36254645b7cc4d81f7c73b2940767fe06de1642c..160cd2f6baf9614b1a6bc55f706e66e3e941ddcc 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -973,6 +973,9 @@ 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);
 

diff --git a/kernel/exit.c b/kernel/exit.c
index e6e01b959a0ef3b3efd0fc0624a3286a57770fc8..ab66cb0510835e8665365e2bdf501dea68d23119 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -828,14 +828,9 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
         * If the parent exec id doesn't match the exec id we saved
         * when we started then we know the parent has changed security
         * domain.
-        *
-        * If our self_exec id doesn't match our parent_exec_id then
-        * we have changed execution domain as these two values started
-        * the same after a fork.
         */
        if (thread_group_leader(tsk) && tsk->exit_signal != SIGCHLD &&
-           (tsk->parent_exec_id != tsk->real_parent->self_exec_id ||
-            tsk->self_exec_id != tsk->parent_exec_id))
+           tsk->parent_exec_id != tsk->real_parent->self_exec_id)
                tsk->exit_signal = SIGCHLD;
 
        if (unlikely(tsk->ptrace)) {