From: Stephen Hemminger <shemminger@osdl•org>
To: shaw@vranix•com
Cc: netdev@vger•kernel.org
Subject: Re: e1000_xmit_frame and e1000_down racing with next_to_use?
Date: Wed, 6 Sep 2006 11:13:25 -0700 [thread overview]
Message-ID: <20060906111325.7acab51a@localhost.localdomain> (raw)
In-Reply-To: <4348.38.114.160.126.1157565495.squirrel@webmail.vranix.com>
On Wed, 6 Sep 2006 10:58:15 -0700 (PDT)
shaw@vranix•com wrote:
> Hello All,
>
> I have a question about the use of the tx_ring->next_to_use variable in
> the e1000. Specifically, I'm wondering about a race between the use of
> next_to_use in e1000_xmit_frame and the clearing of next_to_use in
> e1000_down via e1000_clean_tx_ring.
>
> Thread 1 (_xmit) -> first = adapter->tx_ring.next_to_use;
> e1000_tx_map();
> Thread 2 (_down) -> e1000_clean_tx_ring();
> tx_ring->next_to_use = 0;
> Thread 1 (_xmit) -> e1000_tx_queue();
>
> It seems that tx_ring.next_to_use could change between the time the skbuff
> is mapped in e1000_tx_map and the time it is reported to the hardware in
> e1000_tx_queue. While I don't see any memory leaks or possible oops, it
> does seem possible that that an skbuff could be "lost" in the ring as it
> will not be queued in the subsequent e1000_queue.
>
> If the race is possible, perhaps this could be the culprit behind the tx
> timeouts we've seen reported in this list? The watchdog will eventually
> find the "lost" skbuff and mistakenly think that the hardware transmit has
> hung and stop the queue.
>
> Could one of you plese tell me how this race is avoided, if indeed it is?
>
> Thanks,
> Shaw
>
e1000_down calls netif_stop_queue() and that stops transmit requests.
It doesn't handle the case of a transmit in flight during the e1000_down.
Shouldn't clean_tx_ring acquire tx_ring->tx_lock to avoid that?
--
Stephen Hemminger <shemminger@osdl•org>
next prev parent reply other threads:[~2006-09-06 18:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-06 17:58 e1000_xmit_frame and e1000_down racing with next_to_use? shaw
2006-09-06 18:13 ` Stephen Hemminger [this message]
2006-09-07 0:18 ` Shaw Vrana
2006-09-08 15:51 ` Auke Kok
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