netdev - rhashtable concurrent writers issue, 4.2+

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Message-ID: <566AF520.4000904@canonical.com>
Date:	Fri, 11 Dec 2015 16:09:04 +0000
From:	Colin Ian King <colin.king@...onical.com>
To:	netdev@...r.kernel.org
Cc:	Thomas Graf <tgraf@...g.ch>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: rhashtable concurrent writers issue, 4.2+

Hi,

After testing with commit 7def0f952eccdd0edb3c504f4dab35ee0d3aba1f
("lib: fix data race in rhashtable_rehash_one") on the current 4.4-rc4
kernel, I believe I am still seeing race conditions that seem to bite
concurrent readers.

The reproducer is found in my stress-ng system stress tool:

git://kernel.ubuntu.com/cking/stress-ng.git

one needs libattr1-dev, libkeyutils-dev to build this.

run the concurrent procfs stressor on 2 CPUs:

./stress-ng --procfs 2

..sometimes this hangs w/o a kernel stack dump, but sometimes it oopses
and one can see that we get a concurrent reader failure.

Colin
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