[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Ahmad Samir]

https://bugs.kde.org/show_bug.cgi?id=394360

Ahmad Samir  changed:

   What|Removed |Added

 CC||a.samir...@gmail.com

--- Comment #14 from Ahmad Samir  ---
Might be related to
https://mail.kde.org/pipermail/kde-frameworks-devel/2021-January/115829.html

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Jiri Slaby]

https://bugs.kde.org/show_bug.cgi?id=394360

Jiri Slaby  changed:

   What|Removed |Added

 Resolution|WAITINGFORINFO  |---
 Status|NEEDSINFO   |UNCONFIRMED

--- Comment #13 from Jiri Slaby  ---
(In reply to Jiri Slaby from comment #8)
> I don't want to be too conclusive now, but after quite few plugs/unplugs of
> such kded5:
> # grep -z GLIB /proc/`pidof kded5`/environ; echo
> QT_NO_GLIB=1
> 
> I haven't seen the issue yet.
> 
> But to me it seems that it is enough to just re-run kded5 after power on:
> kquitapp5 kded5; kded5

Correct – it is enough to re-run kded5 like this and kded5 no longer spawns
children. So neither setxkbmap is exec'ed nor other processes. So unless you
have an idea how to run a new (strace'd) instance kded5 which would behave as
the one run by the session, I cannot provide the requested info.

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Fabian Vogt]

https://bugs.kde.org/show_bug.cgi?id=394360

Fabian Vogt  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEEDSINFO
 Resolution|--- |WAITINGFORINFO

--- Comment #12 from Fabian Vogt  ---
Please re-do the strace with "-e trace=rt_sigaction -k" so that we can see
which call chain leads to the glib issue. It might be a bug in Qt, glib, kded
or any of the currently loaded modules.

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Fabian Vogt]

https://bugs.kde.org/show_bug.cgi?id=394360

--- Comment #11 from Fabian Vogt  ---
Reported upstream as https://bugreports.qt.io/browse/QTBUG-69907

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Fabian Vogt]

https://bugs.kde.org/show_bug.cgi?id=394360

--- Comment #10 from Fabian Vogt  ---
(In reply to Michael Pyne from comment #9)
> If glib integration is an issue, there's a separate Qt bug we're tracking
> where timer events can be starved in the glib event loop which may be
> related, at https://bugs.kde.org/show_bug.cgi?id=230184

That's unrelated AFAICT - this issue is about glib removing the SIGCHLD
handler.

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Michael Pyne]

https://bugs.kde.org/show_bug.cgi?id=394360

Michael Pyne  changed:

   What|Removed |Added

 CC||mp...@kde.org

--- Comment #9 from Michael Pyne  ---
If glib integration is an issue, there's a separate Qt bug we're tracking where
timer events can be starved in the glib event loop which may be related, at
https://bugs.kde.org/show_bug.cgi?id=230184

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Jiri Slaby]

https://bugs.kde.org/show_bug.cgi?id=394360

Jiri Slaby  changed:

   What|Removed |Added

 Status|NEEDSINFO   |UNCONFIRMED
 Resolution|WAITINGFORINFO  |---

--- Comment #8 from Jiri Slaby  ---
(In reply to Fabian Vogt from comment #7)
> Please try to run kded5 without the glib event loop:
> 
> kquitapp5 kded5; QT_NO_GLIB=1 kded5
> 
> If that works fine, it's probably a bug in either glib itself or in its
> integration.

I don't want to be too conclusive now, but after quite few plugs/unplugs of
such kded5:
# grep -z GLIB /proc/`pidof kded5`/environ; echo
QT_NO_GLIB=1

I haven't seen the issue yet.

But to me it seems that it is enough to just re-run kded5 after power on:
kquitapp5 kded5; kded5

I haven't seen the issue with such a restart too. But I only tried few replugs.

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Fabian Vogt]

https://bugs.kde.org/show_bug.cgi?id=394360

Fabian Vogt  changed:

   What|Removed |Added

 Resolution|--- |WAITINGFORINFO
 Status|UNCONFIRMED |NEEDSINFO

--- Comment #7 from Fabian Vogt  ---
Please try to run kded5 without the glib event loop:

kquitapp5 kded5; QT_NO_GLIB=1 kded5

If that works fine, it's probably a bug in either glib itself or in its
integration.

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Fabian Vogt]

https://bugs.kde.org/show_bug.cgi?id=394360

--- Comment #6 from Fabian Vogt  ---
That strace output is very useful:

16233 exit_group(0) = ?
16233 +++ exited with 0 +++
13987 <... ppoll resumed> ) = ? ERESTARTNOHAND (To be restarted if
no handler)
13987 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=16233,
si_uid=500, si_status=0, si_utime=0, si_stime=0} ---
13987 ppoll([{fd=-1}, {fd=-1}, {fd=-1}, {fd=46, events=POLLIN}], 4, NULL, NULL,
8 
13990 <... poll resumed> )  = 1 ([{fd=3, revents=POLLIN}])

If I interpret this correctly, kdeinit was currently doing a ppoll (no sigmask,
so == poll) and it had no handler, as otherwise it would've done one of the
calls in the handler and not continue with ppoll.

This seems to explain it:

13987 rt_sigaction(SIGCHLD, {sa_handler=SIG_DFL, sa_mask=[],
sa_flags=SA_RESTORER, sa_restorer=0x7f0242406110}, NULL, 8) = 0

It's the last call to rt_sigaction in that process, so it removed its signal
handler, so it's no surprise it stays a zombie...

Now the question is where the rt_sigaction call comes from. It might be
somewhere in forkfd.

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Jiri Slaby]

https://bugs.kde.org/show_bug.cgi?id=394360

Jiri Slaby  changed:

   What|Removed |Added

 Attachment #112709|0   |1
is obsolete||

--- Comment #5 from Jiri Slaby  ---
Created attachment 114320
  --> https://bugs.kde.org/attachment.cgi?id=114320=edit
strace -f of kded5 (packed by xz due to size)

Now I reproduced even with strace capturing the process. (It still recurs and
is painful.)

13987 is kdeinit.

16233 is the pid of the setxkbmap process which became a zombie.

16213 is the last process which kdeinit called wait4 for. It is another
instance of setxkbmap:
> 16213 exit_group(0) = ? 
> 16213 +++ exited with 0 +++
> 13987 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=16213, 
> si_uid=500, si_status=0, si_utime=0, si_stime=1} ---
> 13987 waitid(P_ALL, 0, {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=16213, 
> si_uid=500, si_status=0, si_utime=0, si_stime=0}, WNOHANG|WEXITED|WNOWAIT, 
> NULL) = 0
> 13987 wait4(16213,  
> 13987 <... wait4 resumed> [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], WNOHANG, 
> {ru_utime={tv_sec=0, tv_usec=2524}, ru_stime={tv_sec=0, tv_usec=10098}, ...}) 
> = 16213

setxkbmap is not the only unreaped process. I also saw zombie of xterm pinned
to kdeinit (opened via ctrl-alt-t which is a custom shortcut to run xterm).

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Jiri Slaby]

https://bugs.kde.org/show_bug.cgi?id=394360

--- Comment #4 from Jiri Slaby  ---
Created attachment 112709
  --> https://bugs.kde.org/attachment.cgi?id=112709=edit
strace -f of kded5 (packed by xz due to size)

I cannot reproduce easily. It happened only once during unplug/replug and not
in this strace run.

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Fabian Vogt]

https://bugs.kde.org/show_bug.cgi?id=394360

--- Comment #3 from Fabian Vogt  ---
 (In reply to Jiri Slaby from comment #2)
> (In reply to Fabian Vogt from comment #1)
> > How well can you reproduce the issue? Can you try to strace -f kded5 while
> > it happens?
> 
> Not really well. Could you tell me what event triggers the stack trace?

connect(xEventNotifier, ::newKeyboardDevice, this,
::configureKeyboard);

i.e. plugging in a keyboard.

> BTW I have just updated to 5.12.5 because I could not find -debuginfo for
> plasma5-desktop-5.12.4 from Tumbleweed anymore. When this happens again, I
> will have better stack trace (#8 and #9 filled in the trace too).

I don't think a more detailed stack trace can help here - an strace would be
ideal.

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Jiri Slaby]

https://bugs.kde.org/show_bug.cgi?id=394360

Jiri Slaby  changed:

   What|Removed |Added

 Status|NEEDSINFO   |UNCONFIRMED
 Resolution|WAITINGFORINFO  |---

--- Comment #2 from Jiri Slaby  ---
(In reply to Fabian Vogt from comment #1)
> How well can you reproduce the issue? Can you try to strace -f kded5 while
> it happens?

Not really well. Could you tell me what event triggers the stack trace?

BTW I have just updated to 5.12.5 because I could not find -debuginfo for
plasma5-desktop-5.12.4 from Tumbleweed anymore. When this happens again, I will
have better stack trace (#8 and #9 filled in the trace too).

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Fabian Vogt]

https://bugs.kde.org/show_bug.cgi?id=394360

Fabian Vogt  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEEDSINFO
 CC||fab...@ritter-vogt.de
 Resolution|--- |WAITINGFORINFO

--- Comment #1 from Fabian Vogt  ---
How well can you reproduce the issue? Can you try to strace -f kded5 while it
happens?

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[frameworks-kded] [Bug 394360] kded5 hangs in QProcess::waitForFinished and does not reap setxkbmap

[Jiri Slaby]

https://bugs.kde.org/show_bug.cgi?id=394360

Jiri Slaby  changed:

   What|Removed |Added

   Platform|Other   |openSUSE RPMs

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