How to debug X lockup (advice from gurus wanted)

Roberto Ragusa mail at
Thu Sep 1 21:05:43 UTC 2011

On 08/30/2011 09:24 PM, stan wrote:
> On Mon, 29 Aug 2011 21:06:29 +0200
> Roberto Ragusa <mail at> wrote:
>> Hi,
>> it sometimes happens to me that X completely locks up, while the
>> machine is still alive on the network.
>> This is on F14, untainted kernel, nouveau driver, no 3D used,
>> KDE desktop on a 32-bit machine with 8GiB RAM and PAE kernel.
>> It typically happens when something is going to be drawn on
>> the screen (a window pops up or virtual desktop change).
>> I would like to open a bug, but I'm not able to attach any kind
>> of usable log; dmesg says nothing, all I can say is that
>> the screen remains frozen (including the pointer), the X
>> server and the kernel keep doing some "SIG ALRM" stuff and
>> any attempt to access the X server stalls the command (xrandr
>> or xset, for example), in a Ctrl-C responsive way.
>> Any idea?
> I had this problem in F14 while using the stock kernel.  When I
> compiled a custom kernel it went away.  While I made *many* changes, I
> think the one that mattered was turning off SMP on my single core
> system.  I suspect, without proof, that the SMP code was occasionally
> causing a race condition, and a deadlock.  Other possible causes for
> fix:  moved to pre-emptable desktop, reserved 128 K low memory for
> kernel, moved to deadline scheduler.
> You could open a bug against the kernel, but it has moved on so far
> that it will probably languish.

[now crossposting fedora, fedora-devel]

Hmmm, turning off SMP is not realistic, as this laptop has a Core 2 Duo.
I had been compiling my kernels until many years ago, and I would like
to stay with the distro's kernel.

I hope that upgrading to F15/F16 will mix things up and solve this in some

Opening a bug seems a waste of time.

I'm cross-posting to fedora-devel, in case someone can suggest how to
collect useful info to open a kernel bug.

   Roberto Ragusa    mail at

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