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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 1 Apr 2020 19:05:59 -0700
Message-ID: <CAHk-=whks0iE1f=Ka0_vo2PYg774P7FA8Y30YrOdUBGRH-ch9A@mail.gmail.com>
Subject: Re: [PATCH] signal: Extend exec_id to 64bits
To:     Jann Horn <jannh@google.com>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Andrea Parri <parri.andrea@gmail.com>,
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        Boqun Feng <boqun.feng@gmail.com>,
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        David Howells <dhowells@redhat.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Akira Yokosawa <akiyks@gmail.com>,
        Daniel Lustig <dlustig@nvidia.com>,
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On Wed, Apr 1, 2020 at 6:36 PM Jann Horn <jannh@google.com> wrote:
>
> Since the read is already protected by the tasklist_lock, an
> alternative might be to let the execve path also take that lock to
> protect the sequence number update,

No.

tasklist_lock is aboue the hottest lock there is in all of the kernel.

We're not doing stupid things for theoretical issues.

Stop this crazy argument.

A comment - sure. 64-bit atomics or very expensive locks? Not a chance.

                   Linus