Re: Crash in GDBM when SDL2 is cleaned-up using atexit

Pekka Paalanen <[email protected]> Mon, 25 Mar 2019 10:13:41 +0200

Newsgroups	gmane.comp.video.mesa3d.user
Message-ID	<[email protected]>

On Sat, 23 Mar 2019 14:28:16 +0100
Sylvain Becker <[email protected]> wrote:

> Hi,
> 
> There is a crash when an SDL2 game (Exult), using KMS-DRM back-end,
> terminates.
> It appears in GBM (gbm_device_destroy()), there migh be also invalid access
> in egl datas.
> 
> SDL2 issue can be found at https://bugzilla.libsdl.org/show_bug.cgi?id=4530
> (with a very small test case)
> Exult game at https://github.com/exult
> 
> It occurs because:
> - Mesa uses atexit()
> - Exult game also chooses atexit() to clean up SDL2 internals. (e.g
> atexit(SDL_Quit))
> 
> Depending on how atexit callbacks are sorted/registered :
> - Mesa cleans up first GBM with an atexit().
> - If SDL2 tries to clean up things once again and it crashes.
> 
> This is reported for SDL2, but any layer using atexit() and GBM could
> reproduce the same crash.
> 
> There are surely several ways to avoid this, but I wonder what you would
> advice to solve this.

Hi,

my personal opinion is that the use of atexit() is almost always a bad
idea, both for the app and Mesa. I'm not a Mesa developer and I don't
know why Mesa wanted to use it, but I can imagine it is a compromise
between bad choices - I'm sure they know the caveats of atexit(). Your
problem is a good example of why atexit() should not be used at all.

It should be much easier to make the game not use atexit(), because it
controls the application main event loop, than Mesa which has no
knowledge of any main loop and therefore cannot reasonably hook up to
its exit sequence on its own.

Thanks,
pq

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