Hi,Oleg
Thanks for your replay.
> To be honest, I don't understand the changelog. It seems that you want
> to uglify the kernel to simplify the debugging of buggy init? Or what?
My patch is for the following purpose:
1. I hope to fix the occurrence of unexpected panic
- [ 24.705390] kernel BUG at include/linux/pid_namespace.h:98!
This problem occurs when both two init threads enter the do_exit,
One of the init thread is syscall sys_exit_group,and set SIGNAL_GROUP_EXIT
The other init thread perform ret_to_user()->get_signal() and found
SIGNAL_GROUP_EXIT is set,then do_group_exit()->do_exit()
Since there are no alive init threads it finally goes to
zap_pid_ns_processes() and BUG().
Timing details are in the changelog.
2. I hope to fix the problem that coredump cannot be parsed after init crash
Before my patch,ever init sub-thread will finish do_exit(),the last
thread will trigger panic().
Except for the thread that triggered the panic,the state(such as
PF_EXITING etc) of the other threads is already exiting,so we can't
parse coredump from fulldump
In fact, when any one init has been set to SIGNAL_GROUP_EXIT, then we
can trigger panic,and prevent other init threads from continuing to
exit
> Nor can I understand the patch. I fail to understand the games with
> SIGNAL_UNKILLABLE and ->siglock.
When first init thread panic,i don't want other init threads to still
exit,this will destroy the state of other init threads.
so i use SIGNAL_UNKILLABLE to mark this stat,prevent other init
threads from continuing to exit
In addition i use siglock to protect tsk->signal->flags.
> And iiuc with this patch the kernel will crash if init's sub-thread execs,
> signal_group_exit() returns T in this case.
Oleg Nesterov <o...@redhat.com> 于2021年3月10日周三 上午2:27写道：
>
> On 03/09, Qianli Zhao wrote:
> >
> > From: Qianli Zhao <zhaoqia...@xiaomi.com>
> >
> > Once any init thread finds SIGNAL_GROUP_EXIT, trigger panic immediately
> > instead of last thread of global init has exited, and do not allow other
> > init threads to exit, protect task/memory state of all sub-threads for
> > get reliable init coredump
>
> To be honest, I don't understand the changelog. It seems that you want
> to uglify the kernel to simplify the debugging of buggy init? Or what?
>
> Nor can I understand the patch. I fail to understand the games with
> SIGNAL_UNKILLABLE and ->siglock.
>
> And iiuc with this patch the kernel will crash if init's sub-thread execs,
> signal_group_exit() returns T in this case.
>
> Oleg.
>
> > [ 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 <zhaoqia...@xiaomi.com>
> > ---
> > We got an init crash issue, but we can't get init coredump from fulldump,
> > we also
> > see BUG() triggered which calling in zap_pid_ns_processes().
> >
> > From crash dump we can get the following information:
> > 1. "Attempted to kill init",init process is killed.
> > - Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00
> > 2. At the same time as init crash, a BUG() triggered in other core.
> > - [ 24.705390] kernel BUG at include/linux/pid_namespace.h:98!
> > 3. When init thread calls exit_mm, the corresponding thread task->mm will
> > be empty, which is not conducive to extracting coredump
> >
> > To fix the issue and save complete coredump, once find init thread is set
> > to SIGNAL_GROUP_EXIT
> > trigger panic immediately,and other child threads are not allowed to exit
> > just wait for reboot
> >
> > PID: 1 TASK: ffffffc973126900 CPU: 7 COMMAND: "init"
> > #0 [ffffff800805ba60] perf_trace_kernel_panic_late at ffffff99ac0bcbcc
> > #1 [ffffff800805bac0] die at ffffff99ac08dc64
> > #2 [ffffff800805bb10] bug_handler at ffffff99ac08e398
> > #3 [ffffff800805bbc0] brk_handler at ffffff99ac08529c
> > #4 [ffffff800805bc80] do_debug_exception at ffffff99ac0814e4
> > #5 [ffffff800805bdf0] el1_dbg at ffffff99ac083298
> > ->Exception
> >
> > /home/work/courbet-r-stable-build/kernel/msm-4.14/include/linux/pid_namespace.h:
> > 98
> > #6 [ffffff800805be20] do_exit at ffffff99ac0c22e8
> > #7 [ffffff800805be80] do_group_exit at ffffff99ac0c2658
> > #8 [ffffff800805beb0] sys_exit_group at ffffff99ac0c266c
> > #9 [ffffff800805bff0] el0_svc_naked at ffffff99ac083cf
> > ->SYSCALLNO: 5e (__NR_exit_group)
> >
> > PID: 552 TASK: ffffffc9613c8f00 CPU: 4 COMMAND: "init"
> > #0 [ffffff801455b870] __delay at ffffff99ad32cc14
> > #1 [ffffff801455b8b0] __const_udelay at ffffff99ad32cd10
> > #2 [ffffff801455b8c0] msm_trigger_wdog_bite at ffffff99ac5d5be0
> > #3 [ffffff801455b980] do_msm_restart at ffffff99acccc3f8
> > #4 [ffffff801455b9b0] machine_restart at ffffff99ac085dd0
> > #5 [ffffff801455b9d0] emergency_restart at ffffff99ac0eb6dc
> > #6 [ffffff801455baf0] panic at ffffff99ac0bd008
> > #7 [ffffff801455bb70] do_exit at ffffff99ac0c257c
> > /home/work/courbet-r-stable-build/kernel/msm-4.14/kernel/exit.c: 842
> > #8 [ffffff801455bbd0] do_group_exit at ffffff99ac0c2644
> > #9 [ffffff801455bcc0] get_signal at ffffff99ac0d1384
> > #10 [ffffff801455be60] do_notify_resume at ffffff99ac08b2a8
> > #11 [ffffff801455bff0] work_pending at ffffff99ac083b8c
> >
> > ---
> > kernel/exit.c | 29 +++++++++++++++++++++--------
> > 1 file changed, 21 insertions(+), 8 deletions(-)
> >
> > diff --git a/kernel/exit.c b/kernel/exit.c
> > index ef2fb929..6b2da22 100644
> > --- a/kernel/exit.c
> > +++ b/kernel/exit.c
> > @@ -758,6 +758,27 @@ void __noreturn do_exit(long code)
> > validate_creds_for_do_exit(tsk);
> >
> > /*
> > + * Once init group is marked for death,
> > + * panic immediately to get a useable coredump
> > + */
> > + if (unlikely(is_global_init(tsk) &&
> > + signal_group_exit(tsk->signal))) {
> > + spin_lock_irq(&tsk->sighand->siglock);
> > + if (!(tsk->signal->flags & SIGNAL_UNKILLABLE)) {
> > + tsk->signal->flags |= SIGNAL_UNKILLABLE;
> > + spin_unlock_irq(&tsk->sighand->siglock);
> > + panic("Attempted to kill init! exitcode=0x%08x\n",
> > + tsk->signal->group_exit_code ?: (int)code);
> > + } else {
> > + /* init sub-thread is dying, just wait for reboot */
> > + spin_unlock_irq(&tsk->sighand->siglock);
> > + futex_exit_recursive(tsk);
> > + set_current_state(TASK_UNINTERRUPTIBLE);
> > + schedule();
> > + }
> > + }
> > +
> > + /*
> > * We're taking recursive faults here in do_exit. Safest is to just
> > * leave this task alone and wait for reboot.
> > */
> > @@ -776,14 +797,6 @@ 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);
> > --
> > 1.9.1
> >
>
