Messages in this thread | | | Date | Fri, 16 May 2014 17:35:30 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] kthreads: kill CLONE_KERNEL, change kernel_thread(kernel_init) to avoid CLONE_SIGHAND |
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On 05/16, Sasha Levin wrote: > > On 04/13/2014 03:56 PM, Oleg Nesterov 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> > > Hi Oleg, > > This patch triggers a hang during boot in my KVM guest.
Hmm... How??? ;)
> There are no > messages or anything, it just hangs right before init is supposed to > start up.
Do you mean kernel_init() hangs somewhere in run_init_process() paths?
> I've narrowed it down a bit, and it's the removal of CLONE_SIGHAND > that's bothering it.
This must not be possible, I bet there is something else which should be fixed.
> Removing CLONE_FS and CLONE_FILES doesn't > cause the hang on boot.
kernel_thread(kernel_init) doesn't use CLONE_FILES ?
Oleg.
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