Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Sat, 20 Apr 2019 13:51:26 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Christian Brauner <christian@brauner.io>
Cc:     Joel Fernandes <joel@joelfernandes.org>,
        Daniel Colascione <dancol@google.com>,
        Jann Horn <jannh@google.com>,
        Florian Weimer <fweimer@redhat.com>,
        kernel list <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Steven Rostedt <rostedt@goodmis.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andrei Vagin <avagin@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>, Michal Hocko <mhocko@suse.com>,
        Nadav Amit <namit@vmware.com>, Serge Hallyn <serge@hallyn.com>,
        Shuah Khan <shuah@kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Taehee Yoo <ap420073@gmail.com>, Tejun Heo <tj@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        kernel-team <kernel-team@android.com>,
        Tycho Andersen <tycho@tycho.ws>
Subject: Re: [PATCH RFC 1/2] Add polling support to pidfd
Message-ID: <20190420115125.GC17468@redhat.com>
References: <20190417130940.GC32622@redhat.com>
 <CAG48ez2Q0t2-rZz8wmGeih=NigYL-CT3+E6NgiPT0AkOQAUPMQ@mail.gmail.com>
 <CEB62F51-E8BF-4EFB-B438-8AF76633FF00@brauner.io>
 <20190419190247.GB251571@google.com>
 <20190419191858.iwcvqm6fihbkaata@brauner.io>
 <20190419194902.GE251571@google.com>
 <CAKOZueu3PzD_QgROXFRs8FvD=HTKJLsHDK9GrUdbFoMzx_7HEA@mail.gmail.com>
 <CAHrFyr4REuKFuARAXnhBC67TGzyDGmMONc7XjfUGvf+Qfm7EuQ@mail.gmail.com>
 <20190419212002.GB44851@google.com>
 <CAHrFyr6qqj-q9nSVuNhFL5WOcuQstAFvaDu2544OpeMe6jawQw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAHrFyr6qqj-q9nSVuNhFL5WOcuQstAFvaDu2544OpeMe6jawQw@mail.gmail.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 04/19, Christian Brauner wrote:
>
> > Just for the exit notification purposes, the states are:
> > if process has exit_state == 0, block.
> > if process is zombie/dead but not reaped, then return POLLIN
> > if process is reaped, then return POLLIN | POLLHUP
>
> Oleg was explicitly against EXIT_ZOMBIE/DEAD thing, no? He said so in a
> prior mail. Has this been addressed?

Yes, please don't use EXIT_XXX codes, nobody should ever use them except the
core kernel exit/wait paths. For example, EXIT_DEAD means that the task auto-
reaps or its parent had to temporary drop tasklist.

Just check ->exit_state != 0 && thread_group_empty(). Note that we need
thread_group_empty() only for the case when the task is traced, in this case
we have an extra notification for debugger which can confuse pidfd_poll().

And of course, everything will differ if/when we will need to monitor the
sub-threads.

And btw I don't think it needs tasklist_lock, but lets discuss this when we
have a new version based on pidfd.

Oleg.