Groups > linux.kernel > #1419491

Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where needed

From	Oleg Nesterov <oleg@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where needed
Date	2016-06-10 16:50 +0200
Message-ID	<rIvUZ-5O9-7@gated-at.bofh.it> (permalink)
References	<rIcIF-1zJ-1@gated-at.bofh.it> <rIoJP-1vU-21@gated-at.bofh.it> <rItJx-4w2-45@gated-at.bofh.it> <rIume-4YI-7@gated-at.bofh.it> <rIume-4YI-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 06/10, Oleg Nesterov wrote:
>
> On 06/10, Andrea Parri wrote:
> >
> > More simply/clean, as you said, maybe; one advantage of keeping
> > the "raw" smp_read_barrier_depends() in get_trampoline_vaddr() is
> > that we can avoid it when area is NULL;
>
> Do you really think it makes sense to optimize out read_barrier_depends here?
>
> It can only be NULL in handle_swbp(), and in this case we are going to do a
> lot of work, and in particular install this xol vma,

Not to mention that alpha doesn't support uprobes, so this all is currently
cosmetic.

> > a similar solution is adopt-
> > ed in kernel/task_work.c:task_work_cancel().
>
> Heh ;) this code was written before we had lockless_dereference(). And I do
> remember I thought that we need such a helper when read_barrier_depends()
> was added.

Plus this code still use ACCESS_ONCE for the same reason. I'll send a simple
patch, it should not conflict with "Update spin_unlock_wait users" from Peter.

Oleg.

Thread

[PATCH] events/uprobes: move smp_read_barrier_depends() where needed Andrea Parri <parri.andrea@gmail.com> - 2016-06-09 20:20 +0200
  Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 09:10 +0200
    Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 14:30 +0200
      Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 15:10 +0200
        Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 16:50 +0200
          Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 21:40 +0200
    Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 15:00 +0200

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