KDBUS and freezing of DBUS-querying applications

KDBUS and freezing of DBUS-querying applications

[Мисбах-Соловьёв Вадим]

Hello!
I'm experiencing a strange issue, when using KDBUS, but I don't know how to 
properly report it and which info I should proide in addition to th one below.

In short, some userspace applications I'm using are freezing for about a 
minute or so, when thy trying to query system bus.


Mostly it hurts me (in my daily workflow) when I trying to open some network 
resource with kde-open5 (or even target application), because KF5 seavily 
depends on DBUS.

But some time ago I even experienced this with "sudo", and even when I tried 
to query system bus with qdbusviwer, it freezed too.


It is pretty hard to trace entire KF5, but talking about issue with sudo, when 
I straced it, I saw frreze on the:

> ppol(fd=9, ...

syscall

and when I looked in lsof, I noticed that fd9 is /sys/fs/kdbus/0-system/bus.

KF5 things also freezing on sending queries to dbus, but I just can't get 
exactly application that freezing (although, if I just open http-links in 
konsole kpart in either yakuake, konsole or kdevelop — any of them also 
freezing on kdbus fd).

To be honest, I'm not traced qdbusviewer, but I'm pretty sure it will show the 
same.


When I recompiling kernel without KDBUS (or move the module somewhere, so that 
SystemD can't autoload it), all that userspace things starting to work like a 
charm, without a freezes and timeouts.

When I enable KDBUS back (either as module or by compile it in the monolithic 
kernel), all the things reproduces again.


I'm tried with both SystemD-216 and SystemD-226.


P.S. I'll be happy to provide any additional info if you'll ask me.


-- 
Best regards,
mva

Re: KDBUS and freezing of DBUS-querying applications

[David Herrmann]

Hi

On Fri, Oct 2, 2015 at 12:53 PM, Мисбах-Соловьёв Вадим <mva@mva.name> wrote:
> Hello!
> I'm experiencing a strange issue, when using KDBUS, but I don't know how to
> properly report it and which info I should proide in addition to th one below.
>
> In short, some userspace applications I'm using are freezing for about a
> minute or so, when thy trying to query system bus.
>
>
> Mostly it hurts me (in my daily workflow) when I trying to open some network
> resource with kde-open5 (or even target application), because KF5 seavily
> depends on DBUS.
>
> But some time ago I even experienced this with "sudo", and even when I tried
> to query system bus with qdbusviwer, it freezed too.
>
>
> It is pretty hard to trace entire KF5, but talking about issue with sudo, when
> I straced it, I saw frreze on the:
>
>> ppol(fd=9, ...
>
> syscall
>
> and when I looked in lsof, I noticed that fd9 is /sys/fs/kdbus/0-system/bus.
>
> KF5 things also freezing on sending queries to dbus, but I just can't get
> exactly application that freezing (although, if I just open http-links in
> konsole kpart in either yakuake, konsole or kdevelop — any of them also
> freezing on kdbus fd).
>
> To be honest, I'm not traced qdbusviewer, but I'm pretty sure it will show the
> same.
>
>
> When I recompiling kernel without KDBUS (or move the module somewhere, so that
> SystemD can't autoload it), all that userspace things starting to work like a
> charm, without a freezes and timeouts.
>
> When I enable KDBUS back (either as module or by compile it in the monolithic
> kernel), all the things reproduces again.
>
>
> I'm tried with both SystemD-216 and SystemD-226.

I'd really appreciate if you open a bug-report on github [1]. This
sounds very much like a user-space issue, rather than a kdbus kernel
issue. However, a few notes:

 - Does the system log contain anything related to dbus? If you're not
sure, care to append the boot-log?
 - Did you compile systemd yourself? You seem to have kdbus enabled by
default, which I'm not aware of any distro doing. Hence, I'd
appreciate if you can use your distro default systemd installation, to
rule out any unrelated configuration issues.
 - What kernel-version / kdbus tree do you use? Do you use your distro
default config?

Thanks
David

[1] http://github.com/systemd/systemd/issues