linux-kernel - [PATCH 0/5] stop_machine: cleanups and fix

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Message-ID: <20150630012931.GA23904@redhat.com>
Date:	Tue, 30 Jun 2015 03:29:31 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>
Cc:	paulmck@...ux.vnet.ibm.com, mingo@...hat.com, der.herr@...r.at,
	dave@...olabs.net, riel@...hat.com, viro@...IV.linux.org.uk,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: [PATCH 0/5] stop_machine: cleanups and fix

On 06/30, Oleg Nesterov wrote:
>
> But let me send some cleanups first. Plus I believe I found another
> stop_machine bug, see the last patch. So I hope these changes make
> sense in any case.

The last patch fixes the bug, I think. Say, stop_one_cpu(X) can race
with _cpu_down(X)->stop_machine() so that the kernel will crash if this
CPU X becomes online again.

The window after cpu_stopper_thread() returns and before smpboot_thread()
calls ->park() is tiny, but still this is possible afaics.

Oleg.

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