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

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Date:	Thu, 19 Jul 2007 21:22:56 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Olaf Kirch <olaf.kirch@...cle.com>
Cc:	"Kok, Auke" <auke-jan.h.kok@...el.com>,
	Jarek Poplawski <jarkao2@...pl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, davem@...emloft.net
Subject: Re: [patch] revert: [NET]: Fix races in net_rx_action vs netpoll

* Olaf Kirch <olaf.kirch@...cle.com> wrote:

> Here's a somewhat drastic modification that should not change any 
> timing, but just verifies whether my patch is to blame at all. Can you 
> give it a try?

> @@ -1027,7 +1027,7 @@ static inline void netif_rx_complete(str
>  	 * But at least it doesn't penalize the non-netpoll
>  	 * code path. */
>  	if (test_bit(__LINK_STATE_POLL_LIST_FROZEN, &dev->state))
> -		return;
> +		BUG();

ok, i tried the patch below, and it gave this (single) warning:

 Calling initcall 0xc02f5c17: init_netconsole+0x0/0x67()
 netconsole: device eth0 not up yet, forcing it
 netconsole: timeout waiting for carrier
 console [netcon0] enabled
 WARNING: at include/linux/netdevice.h:1030 netif_rx_complete()
  [<c0105e3e>] show_trace_log_lvl+0x19/0x2e
  [<c0105f37>] show_trace+0x12/0x14
  [<c0105f4d>] dump_stack+0x14/0x16
  [<c02c4fef>] e1000_clean+0x1f4/0x26f
  [<c03d0f6f>] netpoll_poll+0x8b/0x357
  [<c03d0e80>] netpoll_send_skb+0xe8/0x14c
  [<c03d1502>] netpoll_send_udp+0x258/0x260
  [<c02f5cea>] write_msg+0x53/0x8d
  [<c012c5ba>] __call_console_drivers+0x4e/0x5a
  [<c012c623>] _call_console_drivers+0x5d/0x61
  [<c012cc42>] release_console_sem+0x120/0x1c1
  [<c012d446>] register_console+0x22e/0x236
  [<c02f5c6c>] init_netconsole+0x55/0x67
  [<c05e48e5>] kernel_init+0x154/0x2d9
  [<c0105c53>] kernel_thread_helper+0x7/0x10
  =======================
 e1000: eth0: e1000_watchdog: NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX/TX
 netconsole: network logging started
 initcall 0xc02f5c17: init_netconsole+0x0/0x67() returned 0.
 initcall 0xc02f5c17 ran for 4012 msecs: init_netconsole+0x0/0x67()
 Calling initcall 0xc0600ff9: spi_transport_init+0x0/0x27()
 initcall 0xc0600ff9: spi_transport_init+0x0/0x27() returned 0.

	Ingo

---
 include/linux/netdevice.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-cfs-2.6.23-git.q.prev3/include/linux/netdevice.h
===================================================================
--- linux-cfs-2.6.23-git.q.prev3.orig/include/linux/netdevice.h
+++ linux-cfs-2.6.23-git.q.prev3/include/linux/netdevice.h
@@ -1027,7 +1027,7 @@ static inline void netif_rx_complete(str
 	 * But at least it doesn't penalize the non-netpoll
 	 * code path. */
 	if (test_bit(__LINK_STATE_POLL_LIST_FROZEN, &dev->state))
-		return;
+		WARN_ON(1);
 #endif

 	local_irq_save(flags);
-
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