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    SubjectRe: [RFC, PATCH 1/3] introduce SYS_CLONE_MASK
    On 04/08, Eric W. Biederman wrote:
    >
    > Oleg Nesterov <oleg@tv-sign.ru> writes:
    >
    > > Perhaps it is better to add reparent_kthread() (next patch) to kthread()
    > > and forget about CLONE_KERNEL_THREAD.
    >
    > Please.

    OK, will do tomorrow.

    > > 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.

    No, it doesn't crash. It just doesn't show kernel threads (ps ax is OK).
    I didn't look into the sources, but I guess the reason is that pstree
    assumes that the "root" of the tree is "pid == 1" process.

    I personally think this is acceptable (and Roland seems to think the same).
    Still, to be safe, I'll break this into 2 patches, the first one sets
    ->exit_state, the second re-parents to swapper.

    In fact, we can do some odd things to make pstree happy. We need ->parent
    only because /proc needs some ->parent fields. But I'd prefer to avoid
    these hacks.

    Still, it is sad that we can't have additional flags for kernel_thread().
    However, I agree with your and Roland's objections.

    Oleg.

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