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

From: Michal Hocko <mhocko@kernel.org>
To: christian.koenig@amd.com
Cc: kvm@vger.kernel.org, "Radim Krčmář" <rkrcmar@redhat.com>,
	"Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>,
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	"Andrea Arcangeli" <aarcange@redhat.com>,
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	"Andrew Morton" <akpm@linux-foundation.org>,
	"Felix Kuehling" <felix.kuehling@amd.com>
Subject: Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers
Date: Fri, 24 Aug 2018 14:03:39 +0200	[thread overview]
Message-ID: <20180824120339.GL29735@dhcp22.suse.cz> (raw)
In-Reply-To: <a27ad1a3-34bd-6b7d-fd09-7737ec3c888d@gmail.com>

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