Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [RFC, PATCH 1/3] introduce SYS_CLONE_MASK | Date | Sun, 08 Apr 2007 19:05:29 -0600 |
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Oleg Nesterov <oleg@tv-sign.ru> writes:
> On 04/08, Eric W. Biederman wrote: > >> If we are going to have kernel only flags please use an additional >> argument to do_fork and copy_process. > > Yes, we can do this. But we have a number of architectures which use > sys_clone() to implement kernel_thread(). It would be nice to have an > architecture neutral kernel_thread() implementation as you proposed. > We should change all of them if we want to add a new parameter to > do_fork(). > > Perhaps it is better to add reparent_kthread() (next patch) to kthread() > and forget about CLONE_KERNEL_THREAD.
Please.
> Anyway, re-parenting to swapper breaks pstree, it doesn't show kernel > threads. And if ->parent == /sbin/init, we can't remove us from ->children > (unless we forbid sub-thread-of-init exec). So the only safe change is > set ->exit_state = -1.
Yes. We certainly need ->exit_state = -1. Earlier I had forgotten about second the use of ->children to update the parent pointer of processes when their parent exits.
There is a practical question how much we care about pstree being confused (I assume it doesn't crash). If this is just a confusion issue then I say go for it. PPID == 0 is a very legitimate way to say the kernel is the parent process.
There are a few more cases where we are likely to get PPID == 0 in the future and /sbin/init already has that now. Plus there is a lot of historic precedent. The odd part is PPID = 0 having multiple children.
If we decide maintaining a tree is important I would much rather put init_task on the task_list so we can see it in /proc then go the other way around.
I would like a confirmation that it PPID == 0 is what is confusing pstree just to make certain we haven't half filled in some field in init_task and are thus giving in correct /proc output. But that is all the double checking I would do.
>> Your current scheme also has the bad side that if user space supplied >> a kernel flag it is hard to detect it and return -EINVAL. Which >> limits future expansion. Silently dropping clone flags is a real >> pain, if you are trying to detect if a new flag has been implemented. > > Yes. But that is what we are doing now. copy_process() just ignores > unknown flags.
Agreed. I fixed that in sys_unshare but I should really submit a patch to do the same for sys_clone at some point.
When know flags aren't implemented we certainly return -EINVAL.
Given that this line of work looks to fix the race that messes allows a threaded init to generate unkillable zombies I can probably find some time in the next while to work on it.
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