This may be a nightmare to debug, but I've hit it at least twice now, so it seems worth reporting to see if we can possibly track it down :/ This is on F20, my main desktop system.

Close as I can tell, both times it's happened while building a live image with livecd-creator. Suddenly gnome-shell becomes unresponsive. If I ssh in from another system, I see it consuming 100% CPU; strace shows it trying to read /run/user/1001/dconf/user over and over:

close(-1)                               = -1 EBADF (Bad file descriptor)
open("/home/adamw/.config/dconf/user", O_RDONLY) = 26
fstat(26, {st_mode=S_IFREG|0644, st_size=75655, ...}) = 0
mmap(NULL, 75655, PROT_READ, MAP_PRIVATE, 26, 0) = 0x7f1ec4073000
close(26)                               = 0
munmap(0x7f1ec4073000, 75655)           = 0
access("/run", F_OK)                    = 0
stat("/run", {st_mode=S_IFDIR|0755, st_size=520, ...}) = 0
access("/run/user", F_OK)               = 0
stat("/run/user", {st_mode=S_IFDIR|0755, st_size=120, ...}) = 0
access("/run/user/1001", F_OK)          = 0
stat("/run/user/1001", {st_mode=S_IFDIR|0700, st_size=220, ...}) = 0
access("/run/user/1001/dconf", F_OK)    = 0
stat("/run/user/1001/dconf", {st_mode=S_IFDIR|0700, st_size=60, ...}) = 0
open("/run/user/1001/dconf/user", O_RDWR|O_CREAT, 0600) = -1 EACCES (Permission denied)
write(2, "\n(gnome-shell:27046): dconf-CRIT"..., 142) = 142
close(-1)                               = -1 EBADF (Bad file descriptor)
open("/home/adamw/.config/dconf/user", O_RDONLY) = 26
fstat(26, {st_mode=S_IFREG|0644, st_size=75655, ...}) = 0
mmap(NULL, 75655, PROT_READ, MAP_PRIVATE, 26, 0) = 0x7f1ec4073000
close(26)                               = 0

If I kill shell and let it restart, it gets stuck in the same state.

I believe the file's supposed to be owned by the user (1001 is my regular user account), but it isn't:

[root@adam adamw]# ls -l /run/user/1001/dconf/user 
-rw-------. 1 root root 2 Dec  2 20:47 /run/user/1001/dconf/user

There is something interesting in the journal around 20:47:

Dec 02 20:47:35 adam.happyassassin.net gnome-session[2027]: Window manager warning: Buggy client sent a _NET_ACTIVE_WINDOW message with a timestamp of 0 for 0x2e00029 (live.py.32)
Dec 02 20:47:35 adam.happyassassin.net gnome-session[2027]: Window manager warning: meta_window_activate called by a pager with a 0 timestamp; the pager needs to be fixed.

'live.py' is part of python-imgcreate, part of livecd-creator; it's a pure command-line tool, though, no GUI, so not exactly sure how it fits in.

If I wipe the file and kill the stuck shell process it auto-respawns successfully. The file is created again, now owned by my user (1001).

So, er...any ideas?