Re: Xen BUG at page_alloc.c:1738 (Xen 4.5)

[Major Hayden <major@mhtx.net>]

On 05/20/2015 05:41 AM, Jan Beulich wrote:
> Considering that no-one else is seeing this - is this perhaps connected
> to you building Xen with pre-release gcc 5.0.1? This is also because in
> order for the above to indeed occur, mmio_ro_do_page_fault()'s
> put_page() would need to drop the last reference of a page, yet
> page_get_owner_and_reference() doesn't obtain a reference when
> a page is unallocated (and hence unowned), i.e. normally a page
> would have a refcount of at least 2 here. Hence this would be
> possible only due to a race, but the exact same race to be observed
> on different hardware _and_ under an emulator is extremely unlikely.

That could be a possibility.  There is one Fedora patch[1] to fix a GCC 5 compile error but that's probably unrelated to the crash.

I'm still hunting around to see what I can figure out.

[1] http://pkgs.fedoraproject.org/cgit/xen.git/tree/?h=f22

--
Major Hayden