Messages in this thread Patch in this message | | | From | (Eric W. Biederman) | Date | Fri, 12 Mar 2021 12:23:11 -0600 | Subject | Re: [PATCH V2] exit: trigger panic when global init has exited |
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Qianli Zhao <zhaoqianligood@gmail.com> writes:
> From: Qianli Zhao <zhaoqianli@xiaomi.com> > > When init sub-threads running on different CPUs exit at the same time, > zap_pid_ns_processe()->BUG() may be happened. > And every thread status is abnormal after exit(PF_EXITING set,task->mm=NULL etc), > which makes it difficult to parse coredump from fulldump normally. > In order to fix the above problem, when any one init has been set to SIGNAL_GROUP_EXIT, > trigger panic immediately, and prevent other init threads from continuing to 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@xiaomi.com>
The changelog is much better thank you.
As Oleg pointer out we need to do something like the code below.
diff --git a/kernel/exit.c b/kernel/exit.c index 04029e35e69a..bc676c06ef9a 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -785,15 +785,16 @@ void __noreturn do_exit(long code) sync_mm_rss(tsk->mm); acct_update_integrals(tsk); group_dead = atomic_dec_and_test(&tsk->signal->live); + /* + * If the 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); + } 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); There is still a race that could lead to the BUG in zap_pid_ns_processes. We still have a case where the last two threads of a process call pthread_exit (aka do_exit not do_group_exit in the kernel).
Thread A Thread B do_exit() do_exit()
exit_signals() tsk->flags |= PF_EXITING; group_dead = false; exit_signals() tsk->flags |= PF_EXITING; exit_notify() forget_original_parent find_child_reaper reaper = find_alive_thread() zap_pid_ns_processes() BUG() group_dead = true; if (is_global_init()) panic("Attemted to kill init"); As we are guaranteed to see the panic with my change above I suggest we augment it by simply removing the BUG in zap_pid_ns_processes.
Or maybe not if there is a better way to write the panic code. I don't think having pid namespaces compiled out is a particularly common case. So whatever we can do to keep the code correct and reduce testing.
Eric
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