Bug 356580

Summary:	startplasmacompositor - kwin_wayland - "/usr/lib/startplasma" - hangs at "start_kdeinit_wrapper"
Product:	[Plasma] kwin	Reporter:	James <james>
Component:	wayland-generic	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED FIXED
Severity:	critical	CC:	bhush94, germano.massullo, kdelibs-bugs
Priority:	NOR	Flags:	mgraesslin: ReviewRequest+
Version:	5.5.0
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
URL:	https://git.reviewboard.kde.org/r/126361/
Latest Commit:	http://commits.kde.org/kwin/14b9046ad2ae7d4b9e3ffda996b2112fae3690c4	Version Fixed In:	5.5.1
Sentry Crash Report:

Description James 2015-12-13 00:48:12 UTC

Arch Linux
plasma-workspace 5.5.0-4 - /usr/bin/startplasmacompositor and /usr/lib/startplasma and /usr/bin/ksmserver
kwin 5.5.0-2 - /usr/bin/kwin_wayland
kinit 5.17.0-1 - /usr/lib/kf5/start_kdeinit_wrapper and /usr/bin/kdeinit5

Reproducible: Always

Steps to Reproduce:
/usr/bin/startplasmacompositor begets /usr/bin/kwin_wayland which begets /usr/lib/startplasma, which gets as far as
LD_BIND_NOW=true /usr/lib/kf5/start_kdeinit_wrapper --kded +kcminit_startup
which hangs, and blocks the subsequent /usr/bin/ksmserver.

Actual Results:  
The user will see the splash screen and then only a blank desktop with a working mouse.  Applications can be started from another terminal, or the session can be killed from another terminal, but only if the user remembers to "Ctrl-Alt-F2".  The session cannot be killed from within the Wayland display since the graphic shell never starts.


Martin Gräßlin, at https://git.reviewboard.kde.org/r/124293/, 2015 July, mentions explicitly about "startplasma" that "There's still the problem that it needs a patched kdeinit with OOM_PROTECT disabled."  And again, at https://plus.google.com/+MartinGräßlin/posts/4T3D7bpZESv
Martin mentions "kdeinit dead locks with the oom protection."

 But, the "/usr/bin/kdeinit5" provided by the recent kinit 5.17.0-1 runs as
 /usr/bin/kdeinit5 --oom-pipe 4 --kded +kcminit_startup
apparently with OOM_PROTECT still enabled, *by default*.  We still see in "kinit-5.17.0/src/CMakeLists.txt"
 set(KDEINIT_OOM_PROTECT 1)
which can be seen to apply to src/kdeinit/kinit.cpp, src/start_kdeinit/start_kdeinit.c, and src/start_kdeinit/start_kdeinit_wrapper.c.

Soooooo - In order to allow people to run kwin_wayland, for now, until the OOM problem is resolved, it would seem better to choose
 set(KDEINIT_OOM_PROTECT)
to "unset" KDEINIT_OOM_PROTECT, *as the default* - or, at least provide a big fat end-user visible warning about the use of "startplasmacompositor", with respect to being "available" or "not available".

Also, KDEINIT_OOM_PROTECT cannot be "unset" from the toplevel CMakeLists.txt, so some changes there would also be useful.

Comment 1 James 2015-12-13 23:56:00 UTC

Talking with Martin, there seems to have been some misunderstanding that this OOM issue had something to do with a simultaneously running Xorg server.  After testing, this is not the case.  A KDE Wayland session will run along side a running Xorg server without problem.  And even without a simultaneously running Xorg server, start_kdeinit_wrapper, in /usr/lib/startplasma, *will* hang/freeze unless kinit is compiled with KDEINIT_OOM_PROTECT unset.

Also, there is an AUR package, kinit-nooom, which only patches src/kdeinit/kinit.cpp, and does not touch src/start_kdeinit/start_kdeinit.c or src/start_kdeinit/start_kdeinit_wrapper.c, which seems to have worked-around the problem with kinit-5.16.  I have not tested that myself.

Maybe somebody else would like to look at reset_oom_protect(), at about line 445, and see why this will cause /usr/lib/kf5/start_kdeinit_wrapper to hang?

Comment 2 Martin Flöser 2015-12-15 12:06:46 UTC

Git commit 14b9046ad2ae7d4b9e3ffda996b2112fae3690c4 by Martin Gräßlin.
Committed on 15/12/2015 at 12:03.
Pushed by graesslin into branch 'Plasma/5.5'.

Unblock signals in child processes

We need to unblock the signals blocked with pthread_sigmask.
This caused kdeinit to block, because it relies on SIGUSR1.
FIXED-IN: 5.5.1
REVIEW: 126361

M  +4    -4    main_wayland.cpp
M  +1    -1    rules.cpp
M  +1    -1    useractions.cpp
M  +18   -0    utils.cpp
M  +15   -0    utils.h

http://commits.kde.org/kwin/14b9046ad2ae7d4b9e3ffda996b2112fae3690c4

Comment 3 James 2015-12-15 22:22:02 UTC

One additional patch is required to gain a functioning desktop.  The first issue involves kdeinit5 hanging while waiting on programs in the kwin repository/package:
 https://git.reviewboard.kde.org/r/126361/diff/1?file=422799

That patch will resolve the hang, allowing /usr/lib/startplasma to start ksmserver.  But there will still be a blank and unresponsive desktop with a working mouse cursor.  To finally start the desktop, apply the patch from the plasma-framework repository/package:
 https://git.reviewboard.kde.org/r/126320/

Together, those patches should provide a working desktop.