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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun, 26 Jun 2022 14:20:44 -0700
Message-ID: <CAHk-=wg2t3D4CjdMiNR6Bs6DESgxf2nVwdX-Cv4G4Uhig2isPg@mail.gmail.com>
Subject: Re: [PATCH 1/3] kthread: Remove the flags argument from kernel_thread
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Christian Brauner <brauner@kernel.org>, Tejun Heo <tj@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Michal Hocko <mhocko@suse.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>
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On Sun, Jun 26, 2022 at 12:15 PM Eric W. Biederman
<ebiederm@xmission.com> wrote:
>
> As kthreadd never exists it simply does not matter what kind of exit
> it has.  So for simplicity make it look like everything else and use
> SIGCHLD.

That "never exists" should be "never exits" ;)

But:

> +pid_t kernel_thread(int (*fn)(void *), void *arg)
>  {
> +       unsigned long flags = CLONE_FS | CLONE_FILES | SIGCHLD;
>         struct kernel_clone_args args = {
>                 .flags          = ((lower_32_bits(flags) | CLONE_VM |
>                                     CLONE_UNTRACED) & ~CSIGNAL),

Please just get rid of that 'flags' thing, and the lower_32_bits()
games and write this all as

    pid_t kernel_thread(int (*fn)(void *), void *arg)
    {
        struct kernel_clone_args args = {
                .flags          = CLONE_FS | CLONE_FILES |
                                  CLONE_VM | CLONE_UNTRACED,
                .exit_signal    = SIGCHLD,
                ...

which does that whole thing much more clearly.

              Linus