netdev - Re: [PATCH] net: fix problem in dequeuing from input_pkt

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Date:	Thu, 20 May 2010 06:37:26 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Changli Gao <xiaosuo@...il.com>, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH] net: fix problem in dequeuing from input_pkt_queue

Le mercredi 19 mai 2010 à 19:48 -0700, Tom Herbert a écrit :
> >> It should be okay?  process_backlog only runs in softirq so bottom
> >> halves are already disabled, and I don't think flush_backlog runs out
> >> of an interrupt.
> >>
> >
> > Oh no. It is an IRQ handler.
> >
> Very well, I will fix that.
> 
> Now I'm wondering, though, what the purpose of flush_backlog is...
> since __netif_receive_skb is called with interrupts enabled it's
> obvious flush_backlog won't catch all the skb's that reference the
> device go away.  Is there a reason these packets need to be flushed
> and can't just be processed?

flush_backlog is called when device is dismantled.

No new packets should be generated by the device at this moment.

Could you please split your patch in units, I spent 20 minutes to review
it and come to same conclusion than Changli (need to disable interrupts
as they are currently disabled) and also :

input_queue_head_incr(sd); are _not_ needed in flush_backlog()

We are in the very last moments of the life of the device, in a very
unlikely situation (packets in flight, not already consumed by the cpu),
we are _dropping_ packets, so OOO means nothing at this point. 

In dev_cpu_callback(), you reverse the order of input_pkt_queue /
process_queue.

Thats fine, but should be a single patch, because I am not sure the
input_queue_head_incr() are valid here, since we re-inject these packets
to netif_rx(). Could you clarify this point ?

Thanks !

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