Help with debugging a bug in Konqueror

[Stefano Crocco]

On martedì 14 luglio 2026 10:41:14 Ora legale dell’Europa centrale Jure Repinc 
wrote:
> Dne torek, 14. julij 2026 ob 08:36 je Stefano Crocco napisal(a):
> > On lunedì 13 luglio 2026 23:21:13 Ora legale dell’Europa centrale Albert
> > 
> > Astals Cid wrote:
> > > El dilluns, 13 de juliol del 2026, a les 9:39:58 (Hora d’estiu d’Europa
> > > 
> > > central), Stefano Crocco va escriure:
> > > > On lunedì 13 luglio 2026 08:49:46 Ora legale dell’Europa centrale you
> > 
> > wrote:
> > > > > On Mon, 2026-07-13 at 08:41 +0200, Stefano Crocco wrote:
> > > > > > Hello to everyone,
> > > > > > for the last few weeks, I've randomly encountered what I assume is
> > > > > > a
> > > > > > bug in
> > > > > > Konqueror: I'd like to fix it, because it's rather annoying, but I
> > > > > > don't know
> > > > > > how to debug it to find its cause.
> > > > > > 
> > > > > > The issue is that sometimes Konqueror completely freezes: none of
> > > > > > its
> > > > > > windows
> > > > > > respond to mouse or keyboard. The only way to go on is to kill it.
> > > > > > It's not a
> > > > > > frequent issue: it usually happens once a day or so. Once it has
> > > > > > happened,
> > > > > > however, it's likely to happen again in a short time.
> > > > > > 
> > > > > > I attach a backtrace by attaching gdb to the Konqueror instance
> > > > > > once
> > > > > > the
> > > > > > freeze happens. As you can see, it contains almost nothing from
> > > > > > Konqueror
> > > > > > itself: just two calls near the bottom, the last of which is a
> > > > > > call
> > > > > > to
> > > > > > QApplication::exec(). All other function calls are either inside
> > > > > > KDE
> > > > > > Frameworks or Qt: I'd almost think this is not a problem with
> > > > > > Konqueror if it
> > > > > > were not for the fact that I'm only experiencing the issue with
> > > > > > Konqueror.
> > > > > 
> > > > > Are you sure freeze happens in that thread?
> > > > > 
> > > > > The stacktrace is from the rendering thread. Does Konqueror window
> > > > > get
> > > > > "grayed out" by KWin when it freezes? If it doesn't I'd think the
> > > > > freeze happens in another thread.
> > > > 
> > > > Thanks for the answer. No, the Konqueror  window doesn't look grayed
> > > > out:
> > > > it looks completely normal to the point that often I don't realize it
> > > > has
> > > > frozen until I try to interact with: only at that point I notice that
> > > > all
> > > > parts of the UI don't respond in any way yo mouse or keyboard. If I
> > > > minimize the window, then restore it, its contents aren't drawn so
> > > > that
> > > > it shows the contents of the previously active window.
> > > > 
> > > > > > Given the randomness of the freezes and the fact that the
> > > > > > backtrace
> > > > > > contains
> > > > > > almost no Konqueror-specific calls, I really have no ideas on how
> > > > > > to
> > > > > > proceed to
> > > > > > debug the issue, and I really don't even know what to search on
> > > > > > the
> > > > > > web. Do
> > > > > > you have any advice?
> > > > > > 
> > > > > > Thanks in advance
> > > > > > 
> > > > > > Stefano
> > > > 
> > > > I attach a new backtrace with all threads (compressed because of
> > > > size).
> > > > I
> > > > still can't see anything related to Konqueror. The only thing I can
> > > > notice
> > > > is a mention of QDBus in thread 67, but I still don't know what
> > > > information
> > > > to get from it. Any other ideas?
> > > 
> > > Does it always get stuck in glXSwapBuffers ?
> > > 
> > > That would call for a driver bug possibly?
> > > 
> > > Does using
> > > 
> > > export QT_XCB_FORCE_SOFTWARE_OPENGL=1
> > > 
> > > make it not get stuck?
> > > 
> > > Cheers,
> > > 
> > >   Albert
> > 
> > Thanks for the avice. I've kept the backtraces of three of these
> > situations
> > and all of them show a call to glXSwapBuffers. As soon as I have time,
> > I'll
> > try your suggestion about QT_XCB_FORCE_SOFTWARE_OPENGL even if I fear it
> > would be difficult to determine whether it actually prevents the issue,
> > given its randomness. For example, yesterday morning I experienced it
> > several times but I haven't had it since yesterday afternoon.
> > 
> > Stefano
> 
> I have recently been experiencing the same freezes and I stumbled upon those
> two bug reports in Mesa 3D that may be related to this:
> https://gitlab.freedesktop.org/mesa/mesa/-/work_items/15765
> https://gitlab.freedesktop.org/mesa/mesa/-/work_items/15802
> 
> There is already some merge request merged that might fix it.
> https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/42758
> 
> Will compile Mesa from git and see if it works for my Falkon freezes.
> 
> Have a great time,
> Jure

I tried installing mesa 26.1.4 with the patch from that merge request. Let's 
see if it fixes the issues. If I won't get any more freezes in three days, I'll 
consider the problem solved.

Stefano