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

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Date:   Fri, 23 Nov 2018 12:14:28 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux MM <linux-mm@...ck.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian König <christian.koenig@....com>
Subject: Re: [Intel-gfx] [PATCH 1/3] mm: Check if mmu notifier callbacks are
 allowed to fail

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