netdev - Re: [BUG] net: cpu offline cause napi stall

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20110601163628.GA2418@osiris.boeblingen.de.ibm.com>
Date:	Wed, 1 Jun 2011 18:36:28 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Frank Blaschka <blaschka@...ux.vnet.ibm.com>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [BUG] net: cpu offline cause napi stall

On Wed, Jun 01, 2011 at 02:13:19PM +0200, Eric Dumazet wrote:
> Le mercredi 01 juin 2011 à 12:33 +0200, Frank Blaschka a écrit :
> > Hi Dave, Eric,
> > 
> > during heavy network load we turn off/on cpus.
> > Sometimes this causes a stall on the network device.
> > Digging into the dump I found out following:
> > 
> > napi is scheduled but does not run. From the I/O buffers
> > and the napi state I see napi/rx_softirq processing has stopped
> > because the budget was reached. napi stays in the
> > softnet_data poll_list and the rx_softirq was raised again.
> > 
> > I assume at this time the cpu offline comes in.
> > the rx softirq is raised/moved to another cpu but napi stays in the poll_list
> > of the softnet_data of the now offline cpu.
> > 
> > reviewing dev_cpu_callback (net/core/dev.c) I did not find the poll_list
> > is transfered to the new cpu. Do you think this could cause the stall or
> > did I miss something?
> > 
> > Thx for your help.
> 
> Hi Frank
> 
> I believe you are right, I cant see where the poll_list transfert from
> dead cpu to online cpu is done.
> 
> Do you want to prepare a patch ?

Frank will be offline until next week. I assume the patch below would fix
the problem, however its untested. I doubt we can verify that it really
fixes the problem also until next week (public holiday tomorrow).

diff --git a/net/core/dev.c b/net/core/dev.c
index 6561021..6d6a7cf 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5981,6 +5981,8 @@ static int dev_cpu_callback(struct notifier_block *nfb,
 		oldsd->output_queue = NULL;
 		oldsd->output_queue_tailp = &oldsd->output_queue;
 	}
+	/* Append NAPI poll list from offline CPU. */
+	list_splice_init(&oldsd->poll_list, &sd->poll_list);
 
 	raise_softirq_irqoff(NET_TX_SOFTIRQ);
 	local_irq_enable();
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html