hi Eugene. Provide please your HW information, mesa version and kernel version.
Also would be great to see your Xorg.1.log (if you are using X server).
Your current OS also would be helpful to know.
Thanks.

Created attachment 144422 [details]
lspci

Created attachment 144423 [details]
Xorg.log

$ uname -a
Linux tiger 5.1.5-gentoo #1 SMP PREEMPT Mon May 27 17:27:22 CEST 2019 x86_64 Intel(R) Core(TM) i7-4810MQ CPU @ 2.80GHz GenuineIntel GNU/Linux

Mesa versions 19.1.0 RC1 to RC4, all show the same behaviour. In a Wayland Plasma session everything is extremely clumsy: screen updates irregulary, mouse cursor moves by big leaps (maybe 0.5 second).

thanks. I have hawell based CPU too, with the same GPU on board:
Intel Core i5-4300M 	
Intel® HD Graphics 4600 
Fedora 29

And I can't reproduce this issue. According to your xorg log, you have radeon gpu on board. Could you please check kwin on it?
something like:
>>DRI_PRIME=1 kwin_x11 --replace

With DRI_PRIME kwin does not crash, but not all composite effects can be enabled, so maybe it simply does not touch the crashing path? However, window shadows (the backtrace contains window shadows) are drawn normally.

aha, ok, thanks for this test. One more idea came into mind - try please to make an apitrace of it. I tested it on my machine - and successfully created 2 apitraces, so it is possible.

Command:

>apitrace trace kwin_x11 --replace
To stop tracing use "ctrl + Z" (ctrl+C will crash apitrace and won't generate trace). Also would be helpful to check my apitrace on your HW (I will upload it later).

btw - did you try to disable compositing for windows? In my case I checked both - with and without compositing

Thank you, I'll try to run apitest. In the meantime recompiled mesa with debug options and here is the updated stacktrace:

Application: KWin (kwin_x11), signal: Segmentation fault
 
Thread 1 (Thread 0x7f314646c8c0 (LWP 24002)):
[KCrash Handler]
#5  0x00007f312e10d124 in _mesa_glthread_finish (ctx=0x0) at ../mesa-19.1.0-rc4/src/mesa/main/glthread.c:184
#6  0x00007f312e00a8a4 in intelUnbindContext (driContextPriv=<optimized out>) at ../mesa-19.1.0-rc4/src/mesa/drivers/dri/i965/brw_context.c:1232
#7  0x00007f312e0987ea in driUnbindContext (pcp=0x55acf0ede080) at ../mesa-19.1.0-rc4/src/mesa/drivers/dri/common/dri_util.c:615
#8  0x00007f314ab53425 in dri2_make_current (drv=0x55acee384c30, disp=0x55acf1aecd90, dsurf=0x55acf1c030d0, rsurf=0x55acf1c030d0, ctx=<optimized out>) at ../mesa-19.1.0-rc4/src/egl/drivers/dri2/egl_dri2.c:1479
#9  0x00007f314ab491d7 in eglMakeCurrent (dpy=0x55acf1aecd90, draw=0x55acf1c030d0, read=0x55acf1c030d0, ctx=<optimized out>) at ../mesa-19.1.0-rc4/src/egl/main/eglapi.c:869
#10 0x00007f313e58020e in non-virtual thunk to KWin::AbstractEglBackend::makeCurrent() () from /usr/lib64/qt5/plugins/org.kde.kwin.platforms/KWinX11Platform.so
#11 0x00007f308d61388e in KWin::SceneOpenGLShadow::~SceneOpenGLShadow() () from /usr/lib64/qt5/plugins/org.kde.kwin.scenes/KWinSceneOpenGL.so

(In reply to Denis from comment #7)
> btw - did you try to disable compositing for windows? In my case I checked
> both - with and without compositing

It crashes only with compositing enabled, as I wrote in the bug title. Perhaps you mean something else?

Created attachment 144428 [details]
apitrace

Hello, Eugene.
Could you, please, apply patch '110814_log.diff' and provide dumped log.

Also additionally could you, please, try as workaround: for X11 config similar to '/usr/share/X11/xorg.conf.d/20-intel.conf' apply (for sure its better to reboot):
'''
Section "Device"
  Identifier  "Intel Graphics"
  Driver      "intel"
  Option      "TearFree" "true"
  Option "DRI" "3"
EndSection
'''

Created attachment 144440 [details] [review]
patch-add-log

Created attachment 144443 [details]
stderr log with the patch

Had to change Xorg driver to "intel" from "modesetting" to apply the configuration options. The log is from the the "intel" driver.

One more ask to check with new patch (we can't reproduce it on our side): '110814_log+pfix.diff'
Potentially it contains a fix also or may cause another assert - then will need a new stacktrace

Created attachment 144456 [details] [review]
log+potentialfix

Created attachment 144457 [details]
log with "log+potentialfix" applied

Thank you, with this patch it does not crash and compositing seems to be working fine.

Good, will provide a MR to Mesa soon.
Thanks.

Also confirming this patch fixes a KWin crash with EGL platform interface on my system.

I use the EGL backend too.

https://gitlab.freedesktop.org/mesa/mesa/merge_requests/1020

But it may just hide a some another issue.
So would like to ask for help in collecting more logs with patch '110814_log+ext.diff' (it will crash).

Eugene, could you help with it?

Created attachment 144458 [details] [review]
logs extra

Created attachment 144459 [details]
log extra

Here is the log, please.

and one more question from me, Eugene, provide please output from 
>~/.config/kwinrc

Created attachment 144460 [details]
kwinrc

Maybe you are looking for this too?

$ env | grep KWIN
KWIN_OPENGL_WS=egl

and for this also, yeap. My current config file is match smaller from your's.
I tried to launch kwin with mentioned flag. Everything worked fine also. Will try to apply your config (with some changes related to my PC)

hmmm, looks like I am on  a right way :)
https://gist.github.com/DenKos363/48663a808e8c910bca636a91f6ffa641
I got 1 sig fault, very similar to your's. Investigating and trying to find stable steps

hi, sorry for long reply, but anyway - we could find and reproduce this issue.
Also I made a bisect, and it lead to this commit:

commit dca36d5516d0fdaf012b4476975c5d585c2d1a09
Author: Kenneth Graunke <kenneth@whitecape.org>
Date: Sun Jul 9 23:03:44 2017 -0700

i965: Implement threaded GL support.

Now i965 supports mesa_glthread=true like Gallium drivers do.

According to Markus (degasus), the Citra emulator now runs ~30% faster.
Emmanuel (linkmauve) also reported that the Dolphin emulator improved
by 2.8x on one game. (Both of those still need to be added to drirc.)

An Intel Mesa CI run with mesa_glthread=true appears to be happy.

Bioshock Infinite's benchmark mode seems to be around 15-20% faster
on my Skylake GT4 at 1920x1080.

Tested-by: Markus Wick <markus@selfnet.de>
Tested-by: Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
Tested-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

Also we created a piglit-test, which should trigger and test this bug:
https://gitlab.freedesktop.org/mesa/piglit/merge_requests/87

As I know, right now the only one "work" solution is waiting for review:
https://bugs.freedesktop.org/show_bug.cgi?id=110814#c20

*** Bug 111271 has been marked as a duplicate of this bug. ***

Is there any stopper to get this patch in, KWin crashes in every eglMakeCurrent, that can easy test when you have egl and glx at same time, that's always on modesetting DDX drivers.

Second released version and without this patch, i still can't understand what is the stopper?

(In reply to Anthony from comment #30)
> Second released version and without this patch, i still can't understand
> what is the stopper?

https://bugs.freedesktop.org/show_bug.cgi?id=111444 here is a release tracking ticket. I asked guys to review/add it to the blockers for release, if they decide that it should be added.

fixed by

1dce75c1839f08cfa78400367019f998c258eff5
Author:     Sergii Romantsov <sergii.romantsov@globallogic.com>
CommitDate: Thu Sep 5 09:04:12 2019 -0700

intel/dri: finish proper glthread

KWin was able to get NULL-context in the call
intelUnbindContext. But a call _mesa_glthread_finish
is not resistent to such case.
Case can be catched with steps:
	1. Create both glx and egl contexts
	2. Make glx as current
	3. Make egl as current
	4. Reset glx context
	5. Make egl as current

Solution adds proper finishing of glthread-context
(context will be taken from the requested dri-context
for unbinding, but not from the saved current context).

Piglit-test: https://gitlab.freedesktop.org/mesa/piglit/merge_requests/87

Cc: 19.1 19.2 <mesa-stable@lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110814
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111271
Fixes: dca36d5516d0 (i965: Implement threaded GL support)
Signed-off-by: Sergii Romantsov <sergii.romantsov@globallogic.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>