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

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Message-Id: <20100901.143815.215547115.davem@davemloft.net>
Date:	Wed, 01 Sep 2010 14:38:15 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ben@...adent.org.uk
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-2.6] 3c59x: Remove incorrect locking; correct
 documented lock hierarchy

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.
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