linux-kernel - Re: [PATCH v2] kernel/exit: do panic earlier to get coredump if global init task exit

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Message-ID: <20191217193315.GG2844@hirez.programming.kicks-ass.net>
Date:   Tue, 17 Dec 2019 20:33:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     chenqiwu <qiwuchen55@...il.com>, christian.brauner@...ntu.com,
        mingo@...nel.org, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, chenqiwu@...omi.com
Subject: Re: [PATCH v2] kernel/exit: do panic earlier to get coredump if
 global init task exit

On Tue, Dec 17, 2019 at 04:23:33PM +0100, Oleg Nesterov wrote:
> On 12/17, chenqiwu wrote:
> >
> > But in fact, I think atomic_read()
> > can avoid the racy even if both threads exit in parallel, since it is
> > an atomic operation forever.
> 
> Hmm, not sure I understand. atomic_read() is just READ_ONCE(), it can't be
> re-ordered but that is all.

That, atomic_read() is just a read. It doesn't modify the variable,
therefore there isn't anything 'atomic' even remotely possible.