linux-kernel - Re: Lockup inside of stop_machine() during modprobe aes (was Re: Another AR5008 hang)

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Date:	Thu, 15 Apr 2010 17:22:05 -0400
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ben Gamari <bgamari.foss@...il.com>
Cc:	Johannes Berg <johannes@...solutions.net>,
	linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
	ath9k@...ema.h4ckr.net, Herbert Xu <herbert@...dor.hengli.com.au>
Subject: Re: Lockup inside of stop_machine() during modprobe aes (was Re:
 Another AR5008 hang)

On Tue, 06 Apr 2010 11:08:22 -0700 (PDT) Ben Gamari <bgamari.foss@...il.com> wrote:

> 
> ...
>
> I just built 2.6.34-rc3 with the appropriate fixes for the ACPI thermal lockdep
> issues and have attached the dmesg output of the crash below. It appears that
> modprobe is freezing with a few locks held while inserting aes.ko. In
> particular, it seems that the kernel is deadlocking inside of stop_machine()
> while flushing workqueues.
> 
> ...
>

My guess would be that ieee80211 is calling crypto->request_module()
under rtnl_lock, and the fact that rtnl_lock is held is causing
modprobe->stop_machine to not complete.

> P.S. I am now quite certain that I was mistaken in saying that 2.6.33 was
> affected. This seems to just be a 2.6.34 issue.

OK, thanks, I'll ask Rafael and Maciej to track this as a post-2.6.33
regression, probably wireless.

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