linux-kernel - Re: [PATCH v5.5 10/10] mmap locking API: rename mmap_sem to mmap

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Message-ID: <9c45327f-5542-c033-ec5e-201e9b0583aa@nvidia.com>
Date:   Wed, 20 May 2020 00:32:53 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Michel Lespinasse <walken@...gle.com>
CC:     Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Liam Howlett <Liam.Howlett@...cle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        David Rientjes <rientjes@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, Ying Han <yinghan@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Daniel Jordan <daniel.m.jordan@...cle.com>
Subject: Re: [PATCH v5.5 10/10] mmap locking API: rename mmap_sem to mmap_lock

On 2020-05-19 19:39, Michel Lespinasse wrote:
...
>> That gives you additional options inside internal_get_user_pages_fast(), such
>> as, approximately:
>>
>> if (!(gup_flags & FOLL_FAST_ONLY))
>>          might_lock_read(&current->mm->mmap_lock);
>>
>> ...not that that is necessarily a great idea, seeing as how it merely changes
>> "might lock" into "maybe might lock".  :)
> 
> I think that is completely fine, makes sure everyone not using
> FOLL_FAST_ONLY realizes that the call could block.
> 
> Can I ask you to add that assertion in your patchset ? Based on
> Matthew's feedback, I would do it in my patchset, but it doesn't seem
> worth doing if we know this will conflict with your changes.
> 

Sure, that's no problem. Although it looks like my changes may land
in mmotm first, and then your patchset, so maybe the right move is to
make this change *after* both of those things happen, yes?


thanks,
-- 
John Hubbard
NVIDIA