[kde] [Bug 357348] New: (Blank) Dialog (any application) freezes randomly due to waiting for open("dev/video0", O_RDWR), unplugging webcam solves the issue

[Vyse007 via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=357348

            Bug ID: 357348
           Summary: (Blank) Dialog (any application) freezes randomly due
                    to waiting for open("dev/video0", O_RDWR), unplugging
                    webcam solves the issue
           Product: kde
           Version: 4.14.1
          Platform: Kubuntu Packages
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: sumi200991 at yahoo.co.in

When using a stock install of the latest Kubuntu 15.10, the dialog that pops up
(for example, when confirming from the user if they really want to delete a
file, or if they really want to apply a setting or discard it), the dialog
freezes with no content being displayed inside it (see screenshot for example).
It stays like this for a while, about 15-20 seconds, during which it can still
be resized and moved (but not closed). After a while the content eventually
displays and the dialog behaves normally again. Happens with most applications
on a stock install (Dolphin, Kate, Konsole, etc.)

http://imgur.com/oRAbQET

Reproducible: Always

Steps to Reproduce:
1. Open up systemsettings5, with a USB webcam connected to the computer.
2. Change a setting.
3. Navigate away from the tab where the setting was changed WITHOUT applying
the change. 

Actual Results:  
An empty dialog pops up (transparent), that populates after a certain amount of
time. During this time it can be moved and resized, but not closed.

Expected Results:  
The dialog should be populated right when it pops up.

So I took it upon myself to debug this issue, and opened an application
(systemsettings5, in my case) under strace. When I change a system setting and
then navigate to a different tab, thereby making the confirmation ("do you want
to apply, revert, etc.") dialog appear, I can see that the strace stalls at the
call

open("/dev/video0", O_RDWR)

I guessed that this has something to do with the Logitech USB webcam that I
have, and so I disconnected it to see if the issue changes, and indeed, it
vanished away! All the applications that previously suffered from this work
fine now! I do not understand why the entire framework would be required to
check for an accessible webcam.

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