+ complete_signal-kill-always-true-core_state-signal_group_exit-check.patch added to mm-nonmm-unstable branch

+ complete_signal-kill-always-true-core_state-signal_group_exit-check.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: complete_signal: kill always-true "core_state || !SIGNAL_GROUP_EXIT" check
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     complete_signal-kill-always-true-core_state-signal_group_exit-check.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/complete_signal-kill-always-true-core_state-signal_group_exit-check.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Oleg Nesterov <oleg@redhat.com>
Subject: complete_signal: kill always-true "core_state || !SIGNAL_GROUP_EXIT" check
Date: Sun, 22 Feb 2026 16:24:00 +0100

The "(signal->core_state || !(signal->flags & SIGNAL_GROUP_EXIT))" check
in complete_signal() is not obvious at all, and in fact it only adds
unnecessary confusion: this condition is always true.

prepare_signal() does:

	if (signal->flags & SIGNAL_GROUP_EXIT) {
		if (signal->core_state)
			return sig == SIGKILL;
		/*
		 * The process is in the middle of dying, drop the signal.
		 */
		return false;
	}

This means that "!signal->core_state && (signal->flags &
SIGNAL_GROUP_EXIT)" in complete_signal() is never possible.

If SIGNAL_GROUP_EXIT is set, prepare_signal() can only return true if
signal->core_state is not NULL.

Link: https://lkml.kernel.org/r/aZsfkDhnqJ4s1oTs@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/signal.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/kernel/signal.c~complete_signal-kill-always-true-core_state-signal_group_exit-check
+++ a/kernel/signal.c
@@ -1000,9 +1000,7 @@ static void complete_signal(int sig, str
 	 * Found a killable thread.  If the signal will be fatal,
 	 * then start taking the whole group down immediately.
 	 */
-	if (sig_fatal(p, sig) &&
-	    (signal->core_state || !(signal->flags & SIGNAL_GROUP_EXIT)) &&
-	    !sigismember(&t->real_blocked, sig) &&
+	if (sig_fatal(p, sig) && !sigismember(&t->real_blocked, sig) &&
 	    (sig == SIGKILL || !p->ptrace)) {
 		/*
 		 * This signal will be fatal to the whole group.
_

Patches currently in -mm which might be from oleg@redhat.com are

exit-kill-unnecessary-thread_group_leader-checks-in-exit_notify-and-do_notify_parent.patch
do_notify_parent-sanitize-the-valid_signal-checks.patch
complete_signal-kill-always-true-core_state-signal_group_exit-check.patch