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Date:   Thu, 11 Mar 2021 17:20:25 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, David Rientjes <rientjes@google.com>,
        Ben Gardon <bgardon@google.com>,
        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Dimitri Sivanich <dimitri.sivanich@hpe.com>
Subject: Re: [PATCH] mm/oom_kill: Ensure MMU notifier range_end() is paired
 with range_start()
Message-ID: <YEpDJ/pPioG9ndYX@dhcp22.suse.cz>
References: <20210310213117.1444147-1-seanjc@google.com>
 <20210311002807.GQ444867@ziepe.ca>
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On Wed 10-03-21 20:28:07, Jason Gunthorpe wrote:
> On Wed, Mar 10, 2021 at 01:31:17PM -0800, Sean Christopherson wrote:
> > Invoke the MMU notifier's .invalidate_range_end() callbacks even if one
> > of the .invalidate_range_start() callbacks failed.  If there are multiple
> > notifiers, the notifier that did not fail may have performed actions in
> > its ...start() that it expects to unwind via ...end().  Per the
> > mmu_notifier_ops documentation, ...start() and ...end() must be paired.
> 
> No this is not OK, if invalidate_start returns EBUSY invalidate_end
> should *not* be called.

Yes, this is what I remember when introducing nonblock interface. So I
agree with Jason this patch is not correct. The interface is subtle but
I remember we couldn't come up with something more robust and still
memory with notifiers to be reapable.
-- 
Michal Hocko
SUSE Labs