linux-kernel - Re: [PATCH] mm: check VMA flags to avoid invalid PROT

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Message-ID: <alpine.LSU.2.11.1610071101410.7822@eggly.anvils>
Date:   Fri, 7 Oct 2016 11:16:26 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Lorenzo Stoakes <lstoakes@...il.com>
cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Rik van Riel <riel@...hat.com>,
        Hugh Dickins <hughd@...gle.com>, linux-mm <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        tbsaunde@...aunde.org, robert@...llahan.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: check VMA flags to avoid invalid PROT_NONE NUMA
 balancing

On Fri, 7 Oct 2016, Lorenzo Stoakes wrote:
> On Fri, Oct 07, 2016 at 08:34:15AM -0700, Linus Torvalds wrote:
> > Would you be willing to look at doing that kind of purely syntactic,
> > non-semantic cleanup first?
> 
> Sure, more than happy to do that! I'll work on a patch for this.
> 
> > I think that if we end up having the FOLL_FORCE semantics, we're
> > actually better off having an explicit FOLL_FORCE flag, and *not* do
> > some kind of implicit "under these magical circumstances we'll force
> > it anyway". The implicit thing is what we used to do long long ago, we
> > definitely don't want to.
> 
> That's a good point, it would definitely be considerably more 'magical', and
> expanding the conditions to include uprobes etc. would only add to that.
> 
> I wondered about an alternative parameter/flag but it felt like it was
> more-or-less FOLL_FORCE in a different form, at which point it may as well
> remain FOLL_FORCE :)

Adding Jan Kara (and Dave Hansen) to the Cc list: I think they were
pursuing get_user_pages() cleanups last year (which would remove the
force option from most callers anyway), and I've lost track of where
that all got to.  Lorenzo, please don't expend a lot of effort before
checking with Jan.

Hugh