[Wayland-bugs] [Bug 93750] Xwayland crashes with SIGBUS when processing PutImage

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93750

--- Comment #5 from Jonas Ådahl <jadahl at gmail.com> ---
(In reply to Pekka Paalanen from comment #4)
> (In reply to Jonas Ådahl from comment #2)
> > One thing I noticed was that /run/user/1000/ was 100% full when SIGBUS was
> > hit, but I couldn't see any error messages about failed allocation, but not
> > sure that has anything to do with it.
> 
> I think this is the cause. For an explanation why a full fs causes a SIGBUS,
> see:
> http://cgit.freedesktop.org/wayland/wayland/commit/
> ?id=011b6954031a25de8d9eb39631b6837553bb3cfb
> 
> Can you somehow check if the target memory is indeed mmapped from that fs
> and if so, how does the file get created? This would allow a graceful
> failure at least.

Seems my xwayland is building without posix_fallocate support, so it is most
likely the "on-the-fly ENOSPC" SIGBUS then.

It also seems xwayland will never build with posix_fallocate because it is
missing the configure.ac rule. Will send a patch fixing that, and see if we
managed to fail gracefully.

Should ftruncate even be supported? To support it while being able to fail
gracefully (i.e. not crash) we'd need to add sigbus handlers here and there I
assume.

> 
> I think the next question would be whether the mmap is of the expected size,
> and should something throttle/reclaim somewhere to avoid filling the fs.

We already throttle wl_surface_attach right? So maybe we could just throttle
buffer creation as well will work just fine.

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