linux-kernel - Re: [patch] revert: [NET]: Fix races in net_rx

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Date:	Tue, 17 Jul 2007 10:16:25 +0200
From:	Olaf Kirch <olaf.kirch@...cle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] revert: [NET]: Fix races in net_rx_action vs netpoll

On Monday 16 July 2007 23:40, Linus Torvalds wrote:
>  - The change seems to always set the LIST_FROZEN bit when calling 
>    ->poll(), and at least on e1000, the NAPI poll() routine ends up doing 
>    that netif_rx_complete(), so we're *guaranteed* to always take the 
>    early exit and not do anything.

That is only in the poll_napi case, where netpoll tries to push pending
frames. The default caller for dev->poll() is net_rx_action.

We only ever get into this particular code branch in poll_napi when
the RX_SCHED bit is already set, ie someone put the device on the NAPI
poll_list and raised the softirq. poll_napi is just doing manually what
net_rx_action would do anyway once the softirq is serviced.

>  - The early return from netif_rx_complete() ends up meaning that an 
>    edge-triggered interrupt isn't handled properly, and will this never 
>    happen again, since it never goes away.

Sorry, I may be sitting on my brain this morning, but I don't understand
how skipping netif_rx_complete would affect ACKing of interrupts.

Olaf
-- 
Olaf Kirch  |  --- o --- Nous sommes du soleil we love when we play
okir@....de |    / | \   sol.dhoop.naytheet.ah kin.ir.samse.qurax
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