netdev - Re: RPS vs. hard-irq-context netif

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Date:	Tue, 17 Aug 2010 13:52:30 +0200
From:	Luca Tettamanti <kronos.it@...il.com>
To:	netdev@...r.kernel.org
Cc:	Johannes Berg <johannes@...solutions.net>
Subject: Re: RPS vs. hard-irq-context netif_rx()

> I got the following on a kvm instance I use for testing:
> 
> [ 51.358803] WARNING: at kernel/lockdep.c:2327trace_hardirqs_on_caller+0x167/0x200()
> [ 51.360210] Hardware name: Bochs
> [ 51.360210] Modules linked in:
> [ 51.360210] Pid: 1546, comm: dhclient3 Tainted: G        W 2.6.35-rc6-wl+ #588
> [ 51.360210] Call Trace:
> [ 51.360210]  <IRQ>  [<ffffffff8104e87f>] warn_slowpath_common+0x7f/0xc0
> [ 51.360210]  [<ffffffff8104e8da>] warn_slowpath_null+0x1a/0x20
> [ 51.360210]  [<ffffffff81087977>] trace_hardirqs_on_caller+0x167/0x200
> [ 51.360210]  [<ffffffff81087a1d>] trace_hardirqs_on+0xd/0x10
> [ 51.360210]  [<ffffffff81056ade>] local_bh_enable+0x9e/0x130
> [ 51.360210]  [<ffffffff8139fa82>] netif_rx+0xc2/0x250
> [ 51.360210]  [<ffffffff813146d7>] ei_receive+0x1b7/0x2c0
> [ 51.360210]  [<ffffffff81314ca2>] __ei_interrupt+0x282/0x360
> [ 51.360210]  [<ffffffff81314dce>] ei_interrupt+0xe/0x10
> [ 51.360210]  [<ffffffff810abe85>] handle_IRQ_event+0x85/0x300
> [ 51.360210]  [<ffffffff810aead5>] handle_level_irq+0x95/0x120
> [ 51.360210]  [<ffffffff81005a12>] handle_irq+0x22/0x30
> [ 51.360210]  [<ffffffff814394b3>] do_IRQ+0x73/0xf0
[...]
>So .. where's the bug? I'd point to CONFIG_RPS since it's newest.

Hello,
I just hit the same warning, with 2.6.36-rc1:

[  228.001459] WARNING: at /home/kronos/src/linux-2.6.git/kernel/softirq.c:143 local_bh_enable+0x3c/0x9a()
[  228.004096] Hardware name: F3Sa                
[  228.004175] Modules linked in: [...]
[  228.015974] Pid: 2818, comm: irqbalance Not tainted 2.6.36-rc1 #274
[  228.015974] Call Trace:
[  228.015974]  <IRQ>  [<ffffffff81034b32>] warn_slowpath_common+0x80/0x98
[  228.015974]  [<ffffffff81034b5f>] warn_slowpath_null+0x15/0x17
[  228.015974]  [<ffffffff8103a009>] local_bh_enable+0x3c/0x9a
[  228.015974]  [<ffffffff8120dc16>] netif_rx+0x75/0x145
[  228.015974]  [<ffffffff8115162f>] ? unmap_single+0x4a/0x52
[  228.015974]  [<ffffffff811e7fcd>] atl1_intr+0x96c/0xa35
[  228.015974]  [<ffffffff8104edf4>] ? hrtimer_wakeup+0x0/0x21
[  228.015974]  [<ffffffff810707b2>] handle_IRQ_event+0x20/0x9a
[  228.015974]  [<ffffffff810723ba>] handle_edge_irq+0xf5/0x141
[  228.015974]  [<ffffffff81004d53>] handle_irq+0x83/0x8c
[  228.015974]  [<ffffffff81004332>] do_IRQ+0x5e/0xc4
[  228.015974]  [<ffffffff812843d3>] ret_from_intr+0x0/0xa

CONFIG_TREE_RCU=y
CONFIG_RPS=y

I never saw the warning with 2.6.35 and earlier kernels though.

Luca
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