linux-kernel - Re: [PATCH 0/2] fix vma->anon_vma check for per-VMA locking; fix anon

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Message-Id: <2229115A-23F2-4B6B-800C-7182199DF79D@gmail.com>
Date:   Thu, 27 Jul 2023 13:11:43 -0700
From:   Nadav Amit <nadav.amit@...il.com>
To:     Linus Torvalds <torvalds@...uxfoundation.org>
Cc:     Will Deacon <will@...nel.org>, Jann Horn <jannh@...gle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 0/2] fix vma->anon_vma check for per-VMA locking; fix
 anon_vma memory ordering



> On Jul 27, 2023, at 12:39 PM, Linus Torvalds <torvalds@...uxfoundation.org> wrote:
> 
> On Thu, 27 Jul 2023 at 12:10, Nadav Amit <nadav.amit@...il.com> wrote:
>> 
>> Interesting. I wonder if you considered adding to READ_ONCE() something
>> like:
>> 
>>        asm volatile("" : "+g" (x) );
>> 
>> So later loads (such as baz = *ptr) would reload the updated value.
> 
> Not necessarily a bad idea.  Although I suspect you'd want to add
> *two* of them - on either side - to make sure any previous loads
> wouldn't be moved around it either.

You are right, two are needed.

I’ll give it a shot and see if I see changes to the binary.