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

From: Michal Hocko <mhocko@kernel.org>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: "Chris Wilson" <chris@chris-wilson.co.uk>,
	"Daniel Vetter" <daniel.vetter@ffwll.ch>,
	LKML <linux-kernel@vger.kernel.org>,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	"Intel Graphics Development" <intel-gfx@lists.freedesktop.org>,
	"DRI Development" <dri-devel@lists.freedesktop.org>,
	"Linux MM" <linux-mm@kvack.org>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"David Rientjes" <rientjes@google.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Christian König" <christian.koenig@amd.com>
Subject: Re: [Intel-gfx] [PATCH 1/3] mm: Check if mmu notifier callbacks are allowed to fail
Date: Fri, 23 Nov 2018 12:14:28 +0100	[thread overview]
Message-ID: <20181123111428.GF8625@dhcp22.suse.cz> (raw)
In-Reply-To: <20181123084934.GI4266@phenom.ffwll.local>

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