[ubuntu-x] fdo bug #19034

Bryce Harrington bryce at canonical.com
Wed Apr 8 21:48:10 BST 2009


Hi Tom, thanks for pointing this out and doing the analysis into it.

Would you mind setting up a bug in launchpad against xorg-server so we
can track this (in case of regressions), with a link to that upstream
bug?  Assign to me and I'll try to get it in.

Bryce

On Wed, Apr 08, 2009 at 03:26:38PM -0400, Thomas Jaeger wrote:
> Hi,
> 
> I know this is kind of last-minute, I was hoping that Peter would come
> up with a fix before jaunty comes out, but this is probably not going to
> happen.  The bug in questions is this one:
> 
> http://bugs.freedesktop.org/show_bug.cgi?id=19034
> 
> The issue is associated to slave device cursors, basically an artifact
> of how the xserver-1.6 code is derived from master.  There is no API to
> access device cursors in 1.6, but it turns out that under certain
> circumstances (I'm not exactly sure how this happens but it seems to be
> some kind of race condition between XI and core grabs), it is possible
> that a device cursor will be set anyway.  If it's a regular cursor (that
> is what the bug report was originally about), this is not a problem
> anymore since this will just modify the core cursor, but if it's an
> animated cursor, we're in trouble:  The device cursor will keep
> replacing the core cursor (so the user will notice an animated cursor
> that shouldn't be there), and when the client destroys the animated
> cursor, the device animated cursor will stay active leading to a server
> crash the next time the cursor is updated.  There is a patch attached to
> the fdo bug report that fixes the issue by basically doing the same
> thing for an animated cursor that we do for a regular cursor:  Apply the
> change to the associated master device.  This is safe for 1.6 since this
> code path should never be hit in the first place, but unfortunately,
> this is not the direction that Peter wants to go for master where each
> device has its own sprite (I'm not sure how things are supposed to work
> with animated cursors there).
> 
> The crash happens randomly when an application that grabs an Xi device
> (such as easystroke) is running when clicking on firefox menus, but it's
> fairly easy to reproduce reliably by setting up a timeout gesture in
> easystroke to rotate the cube in compiz via Control+Shift+Button1 and
> invoke the gesture when firefox is loading a page and showing a 'sandbox'.
> 
> The patch is available at
> http://bugs.freedesktop.org/attachment.cgi?id=21710
> 
> It would be great if it could be applied to the ubuntu package.  The
> regression potential is very low: This code path is only hit under very
> specific circumstances and when it is, it basically means that the
> server is going to crash as soon as the client is closed.
> 
> Thanks,
> Tom
> 
> 
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