netdev - Re: [PATCH] [IPV4] route: fix locking in rt_run

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Date:	Mon, 21 Jan 2008 02:40:43 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	joonwpark81@...il.com
Cc:	netdev@...r.kernel.org, dada1@...mosbay.com
Subject: Re: [PATCH] [IPV4] route: fix locking in rt_run_flush()

From: Joonwoo Park <joonwpark81@...il.com>
Date: Tue, 22 Jan 2008 00:08:57 +0900

> The rt_run_flush() can be stucked if it was called while netdev is on the 
> high load.
> It's possible when pushing rtable to rt_hash is faster than pulling
> from it.
> 
> The commands 'ifconfig up or ifconfig mtu' and netif_carrier_on() can
> introduce soft lockup like this:
> 
> [  363.528001] BUG: soft lockup - CPU#0 stuck for 11s! [events/0:9]
> [  363.531492]
> [  363.535027] Pid: 9, comm: events/0 Not tainted (2.6.24-rc8 #14)
> [  363.538837] EIP: 0060:[<c4086a39>] EFLAGS: 00000286 CPU: 0
> [  363.542762] EIP is at kfree+0xa9/0xf0
> ...
> [  363.660815]  [<c42fb0fd>] skb_release_data+0x5d/0x90
> [  363.666989]  [<c42fb7dc>] skb_release_all+0x5c/0xd0
> [  363.673207]  [<c42faf8b>] __kfree_skb+0xb/0x90
> [  363.679474]  [<c42fb029>] kfree_skb+0x19/0x40
> [  363.685811]  [<c4322d87>] ip_rcv+0x27/0x290
> [  363.692223]  [<c4300ae5>] netif_receive_skb+0x255/0x320
> [  363.698759]  [<f88465aa>] e1000_clean_rx_irq+0x14a/0x4f0 [e1000]
> [  363.705456]  [<f88437c2>] e1000_clean+0x62/0x270 [e1000]
> [  363.712217]  [<c43031ee>] net_rx_action+0x16e/0x220
> [  363.719065]  [<c40346d7>] __do_softirq+0x87/0x100
> [  363.726001]  [<c40347a7>] do_softirq+0x57/0x60
> [  363.732979]  [<c4034b4e>] local_bh_enable_ip+0xae/0x100
> [  363.740094]  [<c43e73f5>] _spin_unlock_bh+0x25/0x30
> [  363.747283]  [<c431ec88>] rt_run_flush+0xc8/0xe0
> [  363.754566]  [<c4320c76>] rt_cache_flush+0xd6/0xe0
> [  363.761917]  [<c4350269>] fib_netdev_event+0x89/0xa0
> [  363.769361]  [<c4047d67>] notifier_call_chain+0x37/0x80
> ...
> 
> This patch makes rt_run_flush() to run with softirq is disabled.
> 
> Signed-off-by: Joonwoo Park <joonwpark81@...il.com>

I agree with the analysis of the problem, however not the solution.

This will absolutely kill software interrupt latency.

In fact, we have moved much of the flush work into a workqueue in
net-2.6.25 because of how important that is

We need to find some other way to solve this.

Eric, any ideas?
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