RE: [Bug 1685] 4.6.0 - sig 11 crash in or under __MESA_destroyBuffer

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On Thu, 18 Oct 2007, Marc Aurele La France wrote:
On Mon, 15 Oct 2007, John Lumby wrote:
On Sun, 14 Oct 2007, John Lumby wrote:

Thanks Marc - but it prompted me for pwd.
And this id can happily ssh to another system of mine without pwd prompt.

date;scp -qp /mnt/super9root/root/core.2856.X11crash.20071003122131 jlumby@xxxxxxxxxxxxxxxxxxxxxx:.;date;scp -qp /mnt/super9root/usr/X11R6/bin/XFree86.statload jlumby@xxxxxxxxxxxxxxxxxxxxxx:.;date;
Sun Oct 14 22:10:48 EDT 2007
jlumby@xxxxxxxxxxxxxxxxxxxxxx's password:
Sun Oct 14 22:10:57 EDT 2007
jlumby@xxxxxxxxxxxxxxxxxxxxxx's password:
Sun Oct 14 22:11:00 EDT 2007
/home/lumby:0 ssh -l lumby date
Sun Oct 14 22:19:51 EDT 2007

The problem turned out to be that jlumby wasn't listed in AllowUsers. Please try again.

It worked this time;   They should be there now (I hope)

Thanks.  These were (and still are) _most_ informative.

I've uncovered a real bug here, one that affects not only GLX & Friends, but potentially other extensions also. The bug only occurs on server shutdown or reset. It is a definite candidate for causing this problem, but I can't be sure at this point, given the memory corruption this core file attests to. Fixing it will take some time (on my part). The bug has existed for quite some time, and from what I can tell, still exists not only in our repository, but X.Org's as well. Given that, I request that you update to the L&G sources, which you can get by following the instructions at http://xfree86.org/cvs. I hope to have a patch against that source ready for you to try in the next few days.

Attached is a preliminary fix. As it turns out, this should also apply to 4.6.0, perhaps even 4.5.0.

I say "preliminary" because this only deals with GLX/Mesa. I consider this instance of the problem to only be the tip of the iceberg of a more general design glitch. To fix that glitch, I'd have to change the order some things are done during server termination or reset. Doing so is likely to break several things which will take some time to go through.

This fix does the following:

- Fix initialisation of __GLXscreenInfo structures (not directly related to
  the problem at hand);
- Fix Mesa to complain (on stderr), rather than segfault, when an attempt is
  made to free an unknown buffer;
- Do not free all Mesa buffers upon GLX extension closedown.  Instead these
  will be freed later, at FreeAllResources() time, when the drawable privates
  that reference these buffers are also freed.

Please let me know if this fixes the segfault. Please `scp` to your id on my machine a capture of the server's stderr, the resulting /var/log/XFree86.0.log, and, should the server still segfault, another copy of the server binary and core file.

Thanks.

Marc.

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