netdev - Re: [PATCH net-2.6] 3c59x: Remove incorrect locking; correct documented lock hierarchy

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Message-ID: <1283377631.5323.285.camel@localhost>
Date:	Wed, 01 Sep 2010 22:47:11 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-2.6] 3c59x: Remove incorrect locking; correct
 documented lock hierarchy

On Wed, 2010-09-01 at 14:38 -0700, David Miller wrote:
> From: Ben Hutchings <ben@...adent.org.uk>
> Date: Tue, 31 Aug 2010 01:15:33 +0100
> 
> > vortex_ioctl() was grabbing vortex_private::lock around its call to
> > generic_mii_ioctl().  This is no longer necessary since there are more
> > specific locks which the mdio_{read,write}() functions will obtain.
> > Worse, those functions do not save and restore IRQ flags when locking
> > the MII state, so interrupts will be enabled when generic_mii_ioctl()
> > returns.
> > 
> > Since there is currently no need for any function to call
> > mdio_{read,write}() while holding another spinlock, do not change them
> > to save and restore IRQ flags but remove the specification of ordering
> > between vortex_private::lock and vortex_private::mii_lock.
> > 
> > Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> > ---
> > I've now borrowed a card to test 3c59x on.  I've seen another regression
> > reported <http://bugs.debian.org/586967> after my locking changes, which
> > I can't reproduce.
> 
> I think the lock is necessary, in some form.
> 
> Nothing otherwise protects vp->mii, which is accessed and modified by
> not just this ioctl, but also ethtool operation calls.
> 
> So we can't apply your patch as-is.

Hmm, yes, I forgot that mii caches information in struct mii_if_info.
Let me rethink this.

Ben.

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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