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Date: Tue, 30 Jun 2015 03:29:31 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>
Cc: paulmck@linux.vnet.ibm.com, mingo@redhat.com, der.herr@hofr.at,
        dave@stgolabs.net, riel@redhat.com, viro@ZenIV.linux.org.uk,
        torvalds@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: [PATCH 0/5] stop_machine: cleanups and fix
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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.