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Subject: Re: [PATCH 2/2] mm: prevent gup_fast from racing with COW during fork
To: Jason Gunthorpe <jgg@nvidia.com>
CC: <linux-kernel@vger.kernel.org>, Andrea Arcangeli <aarcange@redhat.com>,
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From: John Hubbard <jhubbard@nvidia.com>
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Date: Mon, 26 Oct 2020 17:35:06 -0700
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On 10/26/20 4:49 PM, Jason Gunthorpe wrote:
> On Fri, Oct 23, 2020 at 10:31:51PM -0700, John Hubbard wrote:
>> On 10/23/20 10:19 PM, John Hubbard wrote:
>>> On 10/23/20 5:19 PM, Jason Gunthorpe wrote:
>> ...
>> If so, it would still be good to wrap the "acquire" and "release"
>> parts of this into functions, IMHO. So we'd end up with,
>> effectively, a lock API anyway.
> 
> What it really needs is a smp_load_mb() to match the existing smp_store_mb(),
> then this implementation wouldn't look so odd.
> 

No argument there!

> It is actually really straightforwad since the write side is under the
> exclusive mmap_lock.
> 

Yes, conceptually it is pretty clean. I'm still wishing there were a small API to
encapsulate such things, but given that there isn't one, I'll take another look
later tonight and attempt to spot any problems with the current patch, as-is.

"Unfortunately", I don't yet see any problems... :)

thanks,
-- 
John Hubbard
NVIDIA