On Mon, Dec 5, 2016 at 11:11 AM, Vegard Nossum <vegard.nossum@gmail.com> wrote:
>
> ------------[ cut here ]------------
> WARNING: CPU: 22 PID: 14012 at mm/shmem.c:2668 shmem_fallocate+0x9a7/0xac0

Ok, good. So that's confirmed as the cause of this problem.

And the call chain that I wanted is obviously completely
uninteresting, because it's call cghain on the other side (the page
fault side) that would show the nested wake queue behavior. I was just
being stupid about it.

I wonder if we have any other places where we just blithely assume
that "wake_up_all()" will actually empty the whole wait queue. It's
_usually_ true, but as noted, nested waiting does happen.

Anyway, can you try this patch instead? It should actually cause the
wake_up_all() to always remove all entries, and thus the WARN_ON()
should no longer happen (and I removed the "list_del()" hackery).

                       Linus