fixed bug in wl_list

[Iskren Chernev]

Second try.

Regards,
Iskren

On Sat, Mar 12, 2011 at 2:28 PM, Marty Jack <martyj19 at comcast.net> wrote:

> I have never encountered a system where it was believed to be desirable to
> allow something to be removed twice.  It is important to keep data
> structures clean.  If anything you would be more likely to see a debugging
> mode where the lists were fully checked after every insert or remove to make
> sure they are internally consistent, especially if they are important to
> keeping the system running.  It's not that much different from memory
> allocation.  A block is allocated, or it is free, and a double free is a
> bug.
>
> On 03/12/2011 07:01 AM, Iskren Chernev wrote:
> > Well, the actual problem is that something was removed twice. And I know
> where this place is, but I couldn't know if you would like to remove
> elements multiple times with no problems, or treat the list very carefully
> and remove elements only once. But then there should be a way to know if an
> element is already in a list or not. So if there is a way to know that, why
> not make a check inside wl_list_remove, just to make sure.
> >
> > I'll fix it the way you want it to be :)
> >
> > Regards,
> > Iskren
> >
> > On Sat, Mar 12, 2011 at 1:07 PM, Marty Jack <martyj19 at comcast.net<mailto:
> martyj19 at comcast.net>> wrote:
> >
> >
> >
> >     On 03/11/2011 07:32 PM, Iskren Chernev wrote:
> >     > Hello,
> >     >
> >     > I found a bug and fixed it with the patch :)
> >     >
> >     > *to reproduce:*
> >     > run compositor on top of x11
> >     >
> >     > repeat
> >     >    run flower
> >     >    drag & drop it a little
> >     >    move the pointer in and out of the compositor/flower
> >     >    Ctrl+C the flower client
> >     >
> >     > it would break eventually
> >     >
> >     > *problem:*
> >     > I found that the linked list surface->destroy_listener_list got
> corrupted at some point (it was not circular any more, strange next/prev
> etc), which causes the crash.
> >     >
> >     > *solution:*
> >     > The problem was in wl_list_remove -- when you erase an element, you
> don't mark it as 'erased', by setting prev/next to NULL for example. Then if
> you erase it again the list becomes corrupt. I nullified the prev/next and
> check in the begining of wl_list_remove for not-in-list elements and just
> ignore them. That seems to fix it.
> >     >
> >     > Regards,
> >     > Iskren
> >     >
> >     >
> >     >
> >     > _______________________________________________
> >     > wayland-devel mailing list
> >     > wayland-devel at lists.freedesktop.org <mailto:
> wayland-devel at lists.freedesktop.org>
> >     > http://lists.freedesktop.org/mailman/listinfo/wayland-devel
> >
> >     Unfortunately your fix only papers over the real problem, which is
> that the list got corrupted at some point.  It would not actually solve the
> problem.  The source of the corruption needs to be located and fixed; it
> could be removing something twice, inserting something twice, or the like.
>  You could push ahead with this if you were interested.
> >     _______________________________________________
> >     wayland-devel mailing list
> >     wayland-devel at lists.freedesktop.org <mailto:
> wayland-devel at lists.freedesktop.org>
> >     http://lists.freedesktop.org/mailman/listinfo/wayland-devel
> >
> >
>
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