Messages in this thread |  | | Date | Mon, 16 Dec 2019 11:27:59 +0100 | From | Christian Brauner <> | Subject | Re: [PATCH v2] kernel/exit: do panic earlier to get coredump if global init task exit |
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On Mon, Dec 16, 2019 at 11:18:44AM +0800, qiwuchen55@gmail.com wrote: > From: chenqiwu <chenqiwu@xiaomi.com> > > When global init task get a chance to be killed, panic will happen in > later calling steps by do_exit()->exit_notify()->forget_original_parent() > ->find_child_reaper() if all init threads have exited. > > However, it's hard to extract the coredump of init task from a kernel > crashdump, since exit_mm() has released its mm before panic. In order > to get the backtrace of init task in userspace, it's better to do panic > earlier at the beginning of exitting route. > > It's worth noting that we must take case of a multi-threaded init exitting > issue. We need the test for is_global_init() && group_dead to ensure that > it is all of init threads exiting and not just the current thread. > > Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
Just a comment and a nit I can fixup myself.
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
Oleg, wdyt?
> --- > changes in v2: > - using is_global_init() && group_dead as panic condition. > - move up group_dead = atomic_dec_and_test(&tsk->signal->live). > - add comment for this change in do_exit(). > --- > kernel/exit.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/kernel/exit.c b/kernel/exit.c > index bcbd598..33364c8 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); > - }
This made me queasy at first but from what I can see this is safe to remove. We could've only gotten here if: task == child_reaper && !find_alive_thread() && pid_ns == init_pid_ns that should be equivalent to the new is_global_init(tsk) && group_dead check, i.e. I think there's no condition we might loose by removing this check.
> > list_for_each_entry_safe(p, n, dead, ptrace_entry) { > list_del_init(&p->ptrace_entry); > @@ -728,6 +724,14 @@ void __noreturn do_exit(long code) > panic("Attempted to kill the idle task!"); > > /* > + * If all threads of global init have exited, do panic imeddiately
Nit: s/imeddiately/immediately/
but I can fix this up when applying.
> + * to get the coredump to find any clue for init task in userspace. > + */ > + group_dead = atomic_dec_and_test(&tsk->signal->live); > + if (unlikely(is_global_init(tsk) && group_dead)) > + panic("Attempted to kill init! exitcode=0x%08lx\n", code); > + > + /* > * If do_exit is called because this processes oopsed, it's possible > * that get_fs() was left as KERNEL_DS, so reset it to USER_DS before > * continuing. Amongst other possible reasons, this is to prevent > @@ -764,7 +768,6 @@ 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) { > #ifdef CONFIG_POSIX_TIMERS > hrtimer_cancel(&tsk->signal->real_timer); > -- > 1.9.1 >
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