Re: [PATCH] rework/fix is_single_threaded()

[Oleg Nesterov <oleg@redhat.com>]

On 07/09, David Howells wrote:
>
> Oleg Nesterov <oleg@redhat.com> wrote:
>
> > David, do you still dislike ->mmap_sem? I didn't see other objections,
> > and again, imho tasklist_lock is worse.
>
> My main objection to taking mmap_sem is that it restricts where the function
> can be used.  It can't, for example, be called by anyone holding a spinlock.

Yes, it is might_sleep().

> Furthermore, the more locks, the more chance of someone accidentally
> deadlocking something.

The current code is not lockless too, tasklist_lock is not free and
can lead too deadlocks as well.

Anyway. I agree it is better to avoid ->mmap_sem, I'll send the patch
in a minute. But I'd really like to do this in a separate patch, the
change is subtle and needs a changelog at least.

> But apart from that, go for it.

Great, thanks. Then I'll make the patch on top.

Oleg.