Commit 146c22ec authored Dec 11, 2019 by chenqiwu Committed by Alistair Delva Jan 03, 2020

UPSTREAM: exit: panic before exit_mm() on global init exit



Currently, when global init and all threads in its thread-group have exited
we panic via:
do_exit()
-> exit_notify()
   -> forget_original_parent()
      -> find_child_reaper()
This makes it hard to extract a useable coredump for global init from a
kernel crashdump because by the time we panic exit_mm() will have already
released global init's mm.
This patch moves the panic futher up before exit_mm() is called. As was the
case previously, we only panic when global init and all its threads in the
thread-group have exited.

Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
[christian.brauner@ubuntu.com: fix typo, rewrite commit message]
Link: https://lore.kernel.org/r/1576736993-10121-1-git-send-email-qiwuchen55@gmail.com


Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
(cherry picked from commit 43cf75d96409a20ef06b756877a2e72b10a026fc)
Bug: 146789558
Change-Id: Icff81267e8c49bf1d332773351d1b47cb8cbac4a
Signed-off-by: Alistair Delva <adelva@google.com>

parent 3fff726c

kernel/exit.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -578,10 +578,6 @@ static struct task_struct find_child_reaper(struct task_struct 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);
		}

		list_for_each_entry_safe(p, n, dead, ptrace_entry) {
		list_del_init(&p->ptrace_entry);
		@@ -846,6 +842,14 @@ void __noreturn do_exit(long code)
		acct_update_integrals(tsk);
		group_dead = atomic_dec_and_test(&tsk->signal->live);
		if (group_dead) {
		/*
		* If the last thread of global init has exited, panic
		* immediately to get a useable coredump.
		*/
		if (unlikely(is_global_init(tsk)))
		panic("Attempted to kill init! exitcode=0x%08x\n",
		tsk->signal->group_exit_code ?: (int)code);

		#ifdef CONFIG_POSIX_TIMERS
		hrtimer_cancel(&tsk->signal->real_timer);
		exit_itimers(tsk->signal);