Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200419141057.621356-1-gladkov.alexey@gmail.com>
 <87ftcv1nqe.fsf@x220.int.ebiederm.org> <87wo66vvnm.fsf_-_@x220.int.ebiederm.org>
 <CAHk-=wgXEJdkgGzZQzBDGk7ijjVdAVXe=G-mkFSVng_Hpwd4tQ@mail.gmail.com>
 <87tv19tv65.fsf@x220.int.ebiederm.org> <CAHk-=wj-K3fqdMr-r8WgS8RKPuZOuFbPXCEUe9APrdShn99xsA@mail.gmail.com>
 <87mu70psqq.fsf@x220.int.ebiederm.org>
In-Reply-To: <87mu70psqq.fsf@x220.int.ebiederm.org>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 24 Apr 2020 13:10:33 -0700
Message-ID: <CAHk-=wgE3JpLqKdwEzce6PyfqT3DVKccuK0H7ixY28CwOUNdmg@mail.gmail.com>
Subject: Re: [PATCH v2 2/2] proc: Ensure we see the exit of each process tid exactly
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Alexey Gladkov <legion@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Alexey Gladkov <gladkov.alexey@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Apr 24, 2020 at 12:54 PM Eric W. Biederman
<ebiederm@xmission.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