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 >