netdev - Re: lock-warning seen on giving rds-info command

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Message-Id: <20111118.124459.1019488665580264734.davem@davemloft.net>
Date:	Fri, 18 Nov 2011 12:44:59 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	kumaras@...lsio.com, netdev@...r.kernel.org,
	venkat.x.venkatsubra@...cle.com
Subject: Re: lock-warning seen on giving rds-info command

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 18 Nov 2011 09:26:42 +0100

> You mean that following sequence triggers a warning ?
> 
> spin_lock_irqsave(&rds_sock_lock, flags);
> ...
> read_lock_bh(&sk->sk_callback_lock);
> read_unlock_bh(&sk->sk_callback_lock);   // HERE
> ...

This sequence has always been disallowed.

BH's are triggered by software, so when you do local_bh_enable() it checks
to make sure you haven't tried to do this with hard IRQs disabled and
triggers the warning if so.

static void __local_bh_enable(unsigned int cnt)
{
	WARN_ON_ONCE(in_irq());
	WARN_ON_ONCE(!irqs_disabled());
 ...
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