netdev - Re: DEBUG_LOCKS_WARN_ON(in_interrupt()) triggering in socket code

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Message-ID: <20150821140900.GB17065@unicorn.suse.cz>
Date:	Fri, 21 Aug 2015 16:09:00 +0200
From:	Michal Kubecek <mkubecek@...e.cz>
To:	"Jason A. Donenfeld" <Jason@...c4.com>
Cc:	Netdev <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: DEBUG_LOCKS_WARN_ON(in_interrupt()) triggering in socket code

On Fri, Aug 21, 2015 at 03:42:33PM +0200, Jason A. Donenfeld wrote:
> Ahhh, interesting, so it turns out you can't do a number of things
> with a read_lock_bh held, because it increases the softirq count.
> Mystery solved.

You must not do anything that can sleep (like taking a mutex) while
holding a rwlock (even for reading) as someone else could call
write_lock() on the same rwlock on the same CPU in the meantime and
would end up spinning indefinitely while waiting for you to release it.

                                                        Michal Kubecek
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