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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 4 Aug 2023 15:49:40 -0700
Message-ID: <CAHk-=wiy125k1dBmQFTGpHwiOqEyrD6xnd4xKWfe97H_HodgDA@mail.gmail.com>
Subject: Re: [PATCH v2 3/3] fork: lock VMAs of the parent process when forking
To:     Mateusz Guzik <mjguzik@gmail.com>
Cc:     Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org,
        regressions@leemhuis.info, bagasdotme@gmail.com,
        jacobly.alt@gmail.com, willy@infradead.org,
        liam.howlett@oracle.com, david@redhat.com, peterx@redhat.com,
        ldufour@linux.ibm.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
        linux-arm-kernel@lists.infradead.org, gregkh@linuxfoundation.org,
        regressions@lists.linux.dev, Jiri Slaby <jirislaby@kernel.org>,
        =?UTF-8?Q?Holger_Hoffst=C3=A4tte?= <holger@applied-asynchrony.com>,
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On Fri, 4 Aug 2023 at 14:46, Mateusz Guzik <mjguzik@gmail.com> wrote:
>
> I don't see it mentioned in the discussion, so at a risk of ruffling
> feathers or looking really bad I'm going to ask: is the locking of any
> use if the forking process is single-threaded? T

Sadly, we've always been able to access the mm from other processes,
so the locking is - I think - unavoidable.

And some of those "access from other processes" aren't even uncommon
or special. It's things like "ps" etc, that do it just to see the
process name and arguments.

            Linus