X intermittent crashes with SIGSEGV when resizing windows

[Henry Gebhardt]

Dear list,

Cygwin/X crashes every few weeks for me (less if gdb is attached). I
(finally) managed to obtain a backtrace from the last crash:

    Thread 1 received signal SIGSEGV, Segmentation fault.
    [Switching to Thread 13992.0x410c]
    miHandleValidateExposures (pWin=0x8001502e0) at
../mi/miwindow.c:221
    221                 if (RegionNotEmpty(&val->after.borderExposed))

The "bt full" output is attached. Also, "thread apply all bt" and the
server log are attached.

I have not, yet, managed to pin down the exact trigger for the crash,
although it is always related to resizing a window to full screen. That
is, I grab the window with the mouse and move it to the top of the
screen, which automatically makes it full screen. Since I don't want it
to go full screen, I immediately double-click the title.

I am running two graphical programs under Windows 10 WSL2 Ubuntu-20.04:
tilix and evince. I export "DISPLAY=:0" .

Thank you for any help!

Best,
Henry

On Mon, 2020-04-20 at 16:08 -0700, Henry Gebhardt wrote:
> On Mon, 2020-04-20 at 18:03 +0100, Jon Turney wrote:
> > On 18/04/2020 04:38, Henry Gebhardt via Cygwin wrote:
> > > Hi,
> > > 
> > > Cygwin/X crashes every few days for me. I managed to obtain a
> > > backtrace
> > > from the last crash (attached). Server log is also included.
> > > 
> > > I have not, yet, managed to pin down the exact trigger for the
> > > crash. I
> > > am running two graphical programs under Windows 10 WSL2 Debian:
> > > tilix
> > > and evince.
> > > 
> > > Thank you for any help.
> > 
> > Thanks for reporting this issue.
> > 
> > I am assuming, although it's not totally clear from your report,
> > that 
> > you are starting the X server with '-listen tcp', and are setting 
> > DISPLAY to localhost:0.0 or similar in your WSL environment.
> 
> Yes, indeed! Also with "-nowgl", but I assume that is irrelevant.
> 
> > 
> > > Thread 1 received signal SIGPIPE, Broken pipe.
> > > [Switching to Thread 2952.0x1144]
> > > 0x000000010053f250 in _XSERVTransSocketWritev (ciptr=0xffffbb18,
> > >     buf=0xffffbc10, size=-17396) at
> > > /usr/include/X11/Xtrans/Xtranssock.c:2382
> > > 2382    /usr/include/X11/Xtrans/Xtranssock.c: No such file or
> > > directory.
> > 
> > I'm not sure this is the actual point of failure (since the X
> > server 
> > should be setting SIGPIPE to be ignored), so you probably need to
> > tell 
> > gdb not to stop on it e.g. 'handle sigpipe ignore'.
> 
> Thank you for this. I will run with sigpipe ignored, and see if I can
> reproduce then. Might be a few days until it triggers.
> 
> > 
> > In any case, a sigpipe here indicates that the X client has already
> > closed when the X server tries to write to it's socket.
> > 
> > Assuming gdb is giving accurate information here, this is also
> > looks 
> > very odd, as a negative value of size (which is used as iovcnt
> > passed
> > to 
> > write) doesn't make a lot of sense.
> 
> 
> Best,
> Henry
> 

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