linux-kernel - Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers

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Message-ID: <20180824120339.GL29735@dhcp22.suse.cz>
Date:   Fri, 24 Aug 2018 14:03:39 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     christian.koenig@....com
Cc:     kvm@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Sudeep Dutt <sudeep.dutt@...el.com>,
        dri-devel@...ts.freedesktop.org, linux-mm@...ck.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Jason Gunthorpe <jgg@...pe.ca>, linux-rdma@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Doug Ledford <dledford@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        xen-devel@...ts.xenproject.org, intel-gfx@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ashutosh Dixit <ashutosh.dixit@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Felix Kuehling <felix.kuehling@....com>
Subject: Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers

On Fri 24-08-18 13:57:52, Christian König wrote:
> Am 24.08.2018 um 13:52 schrieb Michal Hocko:
> > On Fri 24-08-18 13:43:16, Christian König wrote:
[...]
> > > That won't work like this there might be multiple
> > > invalidate_range_start()/invalidate_range_end() pairs open at the same time.
> > > E.g. the lock might be taken recursively and that is illegal for a
> > > rw_semaphore.
> > I am not sure I follow. Are you saying that one invalidate_range might
> > trigger another one from the same path?
> 
> No, but what can happen is:
> 
> invalidate_range_start(A,B);
> invalidate_range_start(C,D);
> ...
> invalidate_range_end(C,D);
> invalidate_range_end(A,B);
> 
> Grabbing the read lock twice would be illegal in this case.

I am sorry but I still do not follow. What is the context the two are
called from? Can you give me an example. I simply do not see it in the
code, mostly because I am not familiar with it.
-- 
Michal Hocko
SUSE Labs