netdev - Re: [RFC] net: napi fix

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Message-ID: <47613E22.6060705@myri.com>
Date:	Thu, 13 Dec 2007 09:13:54 -0500
From:	Andrew Gallatin <gallatin@...i.com>
To:	Joonwoo Park <joonwpark81@...il.com>
CC:	"Kok, Auke" <auke-jan.h.kok@...el.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jgarzik@...ox.com,
	shemminger@...ux-foundation.org,
	Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: [RFC] net: napi fix

Joonwoo Park wrote:
 > 2007/12/13, Kok, Auke <auke-jan.h.kok@...el.com>:
 >> David Miller wrote:
 >>> From: Andrew Gallatin <gallatin@...i.com>
 >>> Date: Wed, 12 Dec 2007 12:29:23 -0500
 >>>
 >>>> Is the netif_running() check even required?
 >>> No, it is not.
 >>>
 >>> When a device is brought down, one of the first things
 >>> that happens is that we wait for all pending NAPI polls
 >>> to complete, then block any new polls from starting.
 >> I think this was previously (pre-2.6.24) not the case, which is why 
e1000 et al
 >> has this check as well and that's exactly what is causing most of the
 >> net_rx_action oopses in the first place. Without the netif_running() 
check
 >> previously the drivers were just unusable with NAPI and prone to 
many races with
 >> down (i.e. touching some ethtool ioctl which wants to do a reset 
while routing
 >> small packets at high numbers). that's why we added the 
netif_running() check in
 >> the first place :)
 >>
 >> There might be more drivers lurking that need this change...
 >>
 >> Auke
 >>
 >
 > Also in my case, without netif_running() check, I cannot do ifconfig 
down.
 > It stucked if packet generator was sending packets.

If the netif_running() check is indeed required to make a device break
out of napi polling and respond to an ifconfig down, then I think the
netif_running() check should be moved up into net_rx_action() to avoid
potential for driver complexity and bugs like the ones you found.

Drew
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