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Date:   Sat, 20 Apr 2019 13:51:26 +0200
From:   Oleg Nesterov <>
To:     Christian Brauner <>
Cc:     Joel Fernandes <>,
        Daniel Colascione <>,
        Jann Horn <>,
        Florian Weimer <>,
        kernel list <>,
        Andy Lutomirski <>,
        Steven Rostedt <>,
        Suren Baghdasaryan <>,
        Linus Torvalds <>,
        Alexey Dobriyan <>,
        Al Viro <>,
        Andrei Vagin <>,
        Andrew Morton <>,
        Arnd Bergmann <>,
        "Eric W. Biederman" <>,
        Kees Cook <>,
        linux-fsdevel <>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <>, Michal Hocko <>,
        Nadav Amit <>, Serge Hallyn <>,
        Shuah Khan <>,
        Stephen Rothwell <>,
        Taehee Yoo <>, Tejun Heo <>,
        Thomas Gleixner <>,
        kernel-team <>,
        Tycho Andersen <>
Subject: Re: [PATCH RFC 1/2] Add polling support to pidfd

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

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


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