linux-kernel - Re: [BUG] kvm: dereference srcu-protected pointer without srcu_read

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Message-ID: <20100420014504.GB17981@amt.cnet>
Date:	Mon, 19 Apr 2010 22:45:04 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org
Subject: Re: [BUG] kvm: dereference srcu-protected pointer without
 srcu_read_lock() held

On Mon, Apr 19, 2010 at 01:08:29PM +0300, Avi Kivity wrote:
> On 04/19/2010 12:58 PM, Lai Jiangshan wrote:
> >Applied the patch I just sent and let CONFIG_PROVE_RCU=y,
> >we can got the following dmesg. And we found that it is
> >because some codes in KVM dereferences srcu-protected pointer without
> >srcu_read_lock() held or update-side lock held.
> >
> >It is not hard to fix, the problem is that:
> >Where is the most proper place to put a srcu_read_lock()?
> >
> >I can not determine the answer, so I report this bug
> >instead of fixing it.
> >
> 
> I think the else branch in complete_pio() should work.  Marcelo?
> 
> Longer term I'd like to see the lock taken at the high levels
> (ioctls, in virt/kvm) and dropped only for guest entry and when we
> explicitly sleep (hlt emulation).
> 
> Note: complete_pio() is gone in the current code.

Yes, this was fixed by 7fb2ea1e6.

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