From: Oleg Nesterov <oleg@redhat.com>
To: chenqiwu <qiwuchen55@gmail.com>
Cc: christian.brauner@ubuntu.com, peterz@infradead.org,
mingo@kernel.org, kernel-team@android.com,
linux-kernel@vger.kernel.org, chenqiwu@xiaomi.com
Subject: Re: [PATCH v2] kernel/exit: do panic earlier to get coredump if global init task exit
Date: Tue, 17 Dec 2019 16:23:33 +0100 [thread overview]
Message-ID: <20191217152333.GC23152@redhat.com> (raw)
In-Reply-To: <20191217145620.GA26585@cqw-OptiPlex-7050>
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.
How can it avoid the race if it is called before atomic_dec_and_test() ?
Again, suppose that we have 2 exiting threads and signal->live == 2. With
your patch each thread does atomic_read() before atomic_dec_and_test(),
both threads can observe atomic_read(signal->live) == 2 simply because
the counter was not decremented yet.
Oleg.
next prev parent reply other threads:[~2019-12-17 15:23 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-16 3:18 [PATCH v2] kernel/exit: do panic earlier to get coredump if global init task exit qiwuchen55
2019-12-16 10:27 ` Christian Brauner
2019-12-16 17:28 ` Oleg Nesterov
2019-12-16 17:44 ` Christian Brauner
2019-12-17 10:50 ` chenqiwu
2019-12-17 14:25 ` Oleg Nesterov
2019-12-17 14:56 ` chenqiwu
2019-12-17 15:23 ` Oleg Nesterov [this message]
2019-12-17 19:33 ` Peter Zijlstra
2019-12-18 8:08 ` chenqiwu
2019-12-17 14:14 ` Oleg Nesterov
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