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Date:   Tue, 27 Apr 2021 15:43:21 +0800
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     harald@skogtun.org, johannes@sipsolutions.net,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [BISECTED] 5.12 hangs at reboot
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Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> At a guess, there is some other sequence that takes the rtnl lock, and
> then takes the wiphy_lock inside of it, and we have a ABBA deadlock.

The most common cause of these lockups is a stray reference on
some kind of a network object, e.g., a socket or some such.  This
then causes the underlying network device to be reference counted
and triggers a lock-up if that network device needs to be removed.

> I _hate_ that stupid rtnl lock. It's come up before. Several times.
> It's probably the most broken lock in the kernel.

Yes, it's the networking equivalent of the BKL.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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