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SubjectRe: process 'stuck' at exit.
On Tue, Dec 10, 2013 at 01:57:49PM -0800, Linus Torvalds wrote:
> On Tue, Dec 10, 2013 at 1:41 PM, Dave Jones <davej@redhat.com> wrote:
> >
> > http://codemonkey.org.uk/junk/trace
>
> Hmm. Ok, so something is calling [__]get_user_pages_fast() and
> put_page() in a loop, but the trace doesn't show what that "something"
> is, because it is itself not ever called.
>
> However, that pattern does seem to imply that the loop is in
> get_futex_key(), because all the other loops I see seem to be calling
> other things as well.
>
> And the __get_user_pages_fast() call implies that it's the THP case
> that triggers the "unlikely(PageTail(page))" case. And anyway,
> otherwise we'd see lock_page()/unlock_page() too.
>
> So it looks like __get_user_pages_fast() fails, and keeps failing.
> Andrea, this is your code, any ideas? Commit a5b338f2b0b1f ("thp:
> update futex compound knowledge") to be exact.

So, a reason that this might only be showing up now, is that in the last
week I added support to trinity to explicitly do huge page mmaps in the children,
whereas before it only ever did that with MAP_SHARED in the main pid, and then
every child inherited them on fork().

Dave



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