netdev - Re: netpoll + xmit

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Message-Id: <1248894478.4545.2822.camel@calx>
Date:	Wed, 29 Jul 2009 14:07:58 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Matt Carlson <mcarlson@...adcom.com>
Subject: Re: netpoll + xmit_lock == deadlock

On Wed, 2009-07-29 at 15:35 +0800, Herbert Xu wrote:
> Hi:
> 
> While working on TX mitigiation, I noticed that while netpoll
> takes care to avoid recursive dead locks on the NAPI path, it
> has no protection against the TX path when calling the poll
> function.
> 
> So if a driver is in the TX path, and a printk occurs, then a
> recursive dead lock can occur if that driver tries to take the
> xmit lock in its poll function to clean up descriptors.
> 
> Fortunately not a lot of drivers do this but at least some are
> vulnerable to it, e.g., tg3.
> 
> So we need to make it very clear that the poll function must
> not take any locks or they must use try_lock if the driver is
> to support netpoll.

What do you propose?

-- 
http://selenic.com : development and support for Mercurial and Linux


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