linux-kernel - Re: [PATCH v2 2/2] proc: Ensure we see the exit of each process tid exactly

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Message-ID: <CAHk-=wgE3JpLqKdwEzce6PyfqT3DVKccuK0H7ixY28CwOUNdmg@mail.gmail.com>
Date:   Fri, 24 Apr 2020 13:10:33 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Alexey Gladkov <legion@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Alexey Gladkov <gladkov.alexey@...il.com>
Subject: Re: [PATCH v2 2/2] proc: Ensure we see the exit of each process tid exactly

On Fri, Apr 24, 2020 at 12:54 PM Eric W. Biederman
<ebiederm@...ssion.com> wrote:
>
> The problem with
>
> remove
> remove
> add
> add
> is:
>
> A lookup that hit between the remove and the add could return nothing.

Argh. Because that thing doesn't actually _search_ the list, it just
wants to pick any (first) entry. So it doesn't actually care what it
gets, just that it gets something.

Ok, I see.

> For PIDTYPE_PID and PIDTYPE_TGID these practically aren't lists but
> pointers to the appropriate task.  Only for PIDTYPE_PGID and PIDTYPE_SID
> do these become lists in practice.

Yeah, that's what confused me. Ok, please add a comment about the
"single-entry list" issue, and I'm happy.

            Linus