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Subject: netif_poll_enable() & barrier
From: Benjamin Herrenschmidt <benh@au1.ibm.com>
To: "David S. Miller" <davem@davemloft.net>
Cc: Linux Kernel list <linux-kernel@vger.kernel.org>, netdev@vger.kernel.org
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Date: Wed, 20 Dec 2006 14:44:12 +1100
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Hi !

I stumbled accross what might be a bug on out of order architecture:

netif_poll_enable() only does a clear_bit(). However,
netif_poll_disable/enable pairs are often used as simili-spinlocks.

(netif_poll_enable() has pretty much spin_lock semantics except that it
schedules instead of looping).

Thus, shouldn't netif_poll_disable() do an smp_wmb(); before clearing
the bit to make sure that any stores done within the poll-disabled
section are properly visible to the rest of the system before clearing
the bit ?

Cheers,
Ben.