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Date: Mon, 29 Mar 2021 10:27:26 +0800
From: Qianli Zhao <zhaoqianligood@...il.com>
To: christian@...uner.io, axboe@...nel.dk, ebiederm@...ssion.com,
oleg@...hat.com, tglx@...utronix.de, pcc@...gle.com
Cc: linux-kernel@...r.kernel.org, zhaoqianli@...omi.com
Subject: [PATCH V4] exit: trigger panic when global init has exited
From: Qianli Zhao <zhaoqianli@...omi.com>
When init sub-threads running on different CPUs exit at the same time,
zap_pid_ns_processe()->BUG() may be happened(timing is as below),move
panic() before set PF_EXITING to fix this problem.
In addition,if panic() after other sub-threads finish do_exit(),
some key variables (task->mm,task->nsproxy etc) of sub-thread will be lost,
which makes it difficult to parse coredump from fulldump,checking SIGNAL_GROUP_EXIT
to prevent init sub-threads exit.
[ 24.705376] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00
[ 24.705382] CPU: 4 PID: 552 Comm: init Tainted: G S O 4.14.180-perf-g4483caa8ae80-dirty #1
[ 24.705390] kernel BUG at include/linux/pid_namespace.h:98!
PID: 552 CPU: 4 COMMAND: "init"
PID: 1 CPU: 7 COMMAND: "init"
core4 core7
... sys_exit_group()
do_group_exit()
- sig->flags = SIGNAL_GROUP_EXIT
- zap_other_threads()
do_exit() //PF_EXITING is set
ret_to_user()
do_notify_resume()
get_signal()
- signal_group_exit
- goto fatal;
do_group_exit()
do_exit() //PF_EXITING is set
- panic("Attempted to kill init! exitcode=0x%08x\n")
exit_notify()
find_alive_thread() //no alive sub-threads
zap_pid_ns_processes()//CONFIG_PID_NS is not set
BUG()
Signed-off-by: Qianli Zhao <zhaoqianli@...omi.com>
---
V4:
- Changelog update
V3:
- Use group_dead instead of thread_group_empty() to test single init exit.
V2:
- Changelog update
- Remove wrong useage of SIGNAL_UNKILLABLE.
- Add thread_group_empty() test to handle single init thread exit
---
kernel/exit.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/kernel/exit.c b/kernel/exit.c
index 04029e3..f95f8dc 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -766,6 +766,17 @@ void __noreturn do_exit(long code)
validate_creds_for_do_exit(tsk);
+ group_dead = atomic_dec_and_test(&tsk->signal->live);
+ /*
+ * If global init has exited,
+ * panic immediately to get a useable coredump.
+ */
+ if (unlikely(is_global_init(tsk) &&
+ (group_dead || (tsk->signal->flags & SIGNAL_GROUP_EXIT)))) {
+ panic("Attempted to kill init! exitcode=0x%08x\n",
+ tsk->signal->group_exit_code ?: (int)code);
+ }
+
/*
* We're taking recursive faults here in do_exit. Safest is to just
* leave this task alone and wait for reboot.
@@ -784,16 +795,8 @@ void __noreturn do_exit(long code)
if (tsk->mm)
sync_mm_rss(tsk->mm);
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);
+ if (group_dead) {
#ifdef CONFIG_POSIX_TIMERS
hrtimer_cancel(&tsk->signal->real_timer);
exit_itimers(tsk->signal);
--
1.9.1
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