Re: [PATCH] Export current_is_keventd() for libphy

Andrew Morton
2006-12-07T10:43:15Z

> On Thu, 07 Dec 2006 10:29:39 +0000 David Howells <dhowells@redhat.com> wrote:
> Andrew Morton <akpm@osdl.org> wrote:
>
> > I guess I don't understand exactly what problem the noautorel stuff is
> > trying to solve. It _seems_ to me that in all cases we can simply stuff
> > the old `data' field in alongside the controlling work_struct or
> > delayed_work which wants to operate on it.
>
> The problem is that you have to be able to guarantee that the data is still
> accessible once you clear the pending bit. The pending bit is your only
> guaranteed protection, and once it is clear, the containing structure might be
> deallocated.
>
> I would like to be able to get rid of the NAR bit too, but I'm not confident
> that in all cases I can. It'll take a bit more study of the code to be able
> to do that.
>

But anyone who is going to free the structure which contains the
work_struct would need to run flush_workqueue() beforehand, after having
ensured that the work won't reschedule itself. So the
struct-which-contains-the-work_struct is safe during the callback's
execution.

If that's not being done then the code was buggy in 2.6.19, too..