Date: Tue, 31 Jan 2006 15:20:17 -0800 (PST)
From: Linus Torvalds <torvalds@osdl.org>
To: Alexey Dobriyan <adobriyan@gmail.com>
cc: Ingo Molnar <mingo@elte.hu>, "Paul E. McKenney" <paulmck@us.ibm.com>,
       linux-kernel@vger.kernel.org
Subject: Re: Badness in local_bh_enable by [PATCH] fix uidhash_lock <-> RCU
 deadlock
In-Reply-To: <20060131230926.GA7726@mipter.zuzino.mipt.ru>
Message-ID: <Pine.LNX.4.64.0601311512230.7301@g5.osdl.org>
References: <20060131230926.GA7726@mipter.zuzino.mipt.ru>
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On Wed, 1 Feb 2006, Alexey Dobriyan wrote:
>
> Flooding boot logs with
> 
> Badness in local_bh_enable at kernel/softirq.c:140

Ok, looks bad. It's through

    __dequeue_signal():
	collect_signal():
	    __sigqueue_free():
		free_uid()

where we hold the sigqueue lock. We do _not_ want to do BH processing 
there with the lock held and interrupts disabled, so the warning is 
correct, and that uidhash_lock patch potentially causes more problems than 
it fixes.

Perhaps the easiest solution is to just make them irq-safe instead 
of bh-safe? An alternative might be to make __sigqueue_free() do its work 
through RCU callbacks too, but that seems wrong.

Comments? Ingo?

		Linus
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