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SubjectRe: [PATCH] kthreads: kill CLONE_KERNEL, change kernel_thread(kernel_init) to avoid CLONE_SIGHAND
On Sun, 13 Apr 2014 21:56:17 +0200
Oleg Nesterov <oleg@redhat.com> wrote:

> 1. Remove CLONE_KERNEL, it has no users and it is dangerous.
>
> The (old) comment says "List of flags we want to share for kernel
> threads" but this is not true, we do not want to share ->sighand by
> default. This flag can only be used if the caller is sure that both
> parent/child will never play with signals (say, allow_signal/etc).
>
> 2. Change rest_init() to clone kernel_init() without CLONE_SIGHAND.
>
> In this case CLONE_SIGHAND does not really hurt, and it looks like
> optimization because copy_sighand() can avoid kmem_cache_alloc().
>
> But in fact this only adds the minor pessimization. kernel_init()
> is going to exec the init process, and de_thread() will need to
> unshare ->sighand and do kmem_cache_alloc(sighand_cachep) anyway,
> but it needs to do more work and take tasklist_lock and siglock.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---

Looks fine to me.

-- Steve


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