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SubjectApplied patch "exit: panic before exit_mm() on global init exit"
Date
I've added the patch:

exit: panic before exit_mm() on global init exit

to
https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/log/?h=fixes

I've rewritten the commit message and fixed a typo in the comment.

If noone objects this will be part of the threads-fixes pr early next week.

Thanks!
Christian

From 43cf75d96409a20ef06b756877a2e72b10a026fc Mon Sep 17 00:00:00 2001
From: chenqiwu <chenqiwu@xiaomi.com>
Date: Thu, 19 Dec 2019 14:29:53 +0800
Subject: [PATCH] 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>
---
kernel/exit.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index a46a50d67002..fc364272759d 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -517,10 +517,6 @@ 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);
@@ -786,6 +782,14 @@ 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);
--
2.24.0
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