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

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Message-ID: <20110601103356.GA45482@tuxmaker.boeblingen.de.ibm.com>
Date:	Wed, 1 Jun 2011 12:33:56 +0200
From:	Frank Blaschka <blaschka@...ux.vnet.ibm.com>
To:	davem@...emloft.net, eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, linux-s390@...r.kernel.org,
	heiko.carstens@...ibm.com
Subject: [BUG] net: cpu offline cause napi stall

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.

Frank

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