linux-kernel - Re: [PATCH v2 3/3] fork: lock VMAs of the parent process when forking

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Message-ID: <CAHk-=wiy125k1dBmQFTGpHwiOqEyrD6xnd4xKWfe97H_HodgDA@mail.gmail.com>
Date:   Fri, 4 Aug 2023 15:49:40 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Mateusz Guzik <mjguzik@...il.com>
Cc:     Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org,
        regressions@...mhuis.info, bagasdotme@...il.com,
        jacobly.alt@...il.com, willy@...radead.org,
        liam.howlett@...cle.com, david@...hat.com, peterx@...hat.com,
        ldufour@...ux.ibm.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, gregkh@...uxfoundation.org,
        regressions@...ts.linux.dev, Jiri Slaby <jirislaby@...nel.org>,
        Holger Hoffstätte <holger@...lied-asynchrony.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 3/3] fork: lock VMAs of the parent process when forking

On Fri, 4 Aug 2023 at 14:46, Mateusz Guzik <mjguzik@...il.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