Re: [Intel-gfx] [PATCH 1/3] mm: Check if mmu notifier callbacks are allowed to fail

Michal Hocko
2018-11-23T11:14:32Z

On Fri 23-11-18 09:49:34, Daniel Vetter wrote:
> On Thu, Nov 22, 2018 at 04:53:34PM +0000, Chris Wilson wrote:
> > Quoting Daniel Vetter (2018-11-22 16:51:04)
> > > Just a bit of paranoia, since if we start pushing this deep into
> > > callchains it's hard to spot all places where an mmu notifier
> > > implementation might fail when it's not allowed to.
> >
> > Most callers could handle the failure correctly. It looks like the
> > failure was not propagated for convenience.
>
> I have no idea whether the mm is semantically ok if pte shootdown doesn't
> work for all sorts of strange reasons. From the commit that introduced the
> error code it souded like this was very much only ok in the limited case
> of an already killed process, in the oom killer path, where it's really
> only about trying to free any kind of memory. And where the process is
> gone already, so semantics of what exactly happens don't matter that much
> anymore.

Yes this was indeed the case. There is still the exit path which would
do the rest of the work so we are not leaving anything behind.
--
Michal Hocko
SUSE Labs