From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Lameter <cl@linux.com>
Subject: Re: netfilter: Hung task
Date: Mon, 19 Mar 2012 15:03:14 -0500 (CDT)
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Cc: Pablo Neira Ayuso <pablo@netfilter.org>, kaber@trash.net,
	davem@davemloft.net, Dave Jones <davej@redhat.com>,
	netfilter-devel@vger.kernel.org,
	"linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>,
	netdev@vger.kernel.org
To: Sasha Levin <levinsasha928@gmail.com>
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On Mon, 19 Mar 2012, Sasha Levin wrote:

> lockdep listed all the held locks there.

None of the locks listed are slub locks.

> I've mentioned that it looks very similar to
> https://lkml.org/lkml/2012/1/14/45 where the userspace helper tried to
> read from the sysfs files, but got into a deadlock since the kernel
> side held them before it called the usermode helper.

Ah yes. In that case slub held a semaphore. Code was changed since then to
no longer hold a semaphore when calling into sysfs.

The uevent handler can execute arbitrary user space code. Do you have to
hold locks while calling kmem_cache_destroy?