Created attachment 123093 [details]
Stack trace of the crash

Here is a more useful stack trace of this crash, where we can see pointer->focus_client is NULL.

This issue is actually Weston trying to send axis events to clients not having any wl_pointer bound, which leads to this crash.  It also happens when simply scrolling over weston-simple-shm.

This should fix it: https://patchwork.freedesktop.org/patch/82561/

Fixed by:

commit ed6014a9e481772580f7eb9fc7a1200aca7aec5c
Author: Jonas Ådahl <jadahl@gmail.com>
Date:   Thu Apr 21 10:21:48 2016 +0800

    input: Don't try to send axis_source when there are no resources
    
    The focus_client pointer may be NULL here if the focused client has no
    pointer resources. To avoid a crash, NULL check focus client before
    proceeding to send the events.
    
    https://bugs.freedesktop.org/show_bug.cgi?id=94899
    
    Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
    Reviewed-by: Mike Blumenkrantz <zmike@osg.samsung.com>