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Message-ID: <48647B94.5000006@pobox.com>
Date: Fri, 27 Jun 2008 01:33:08 -0400
From: Jeff Garzik <jgarzik@...ox.com>
To: Ingo Molnar <mingo@...e.hu>
CC: Michael Buesch <mb@...sch.de>,
Johannes Berg <johannes@...solutions.net>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Linux Kernel list <linux-kernel@...r.kernel.org>,
David Ellingsworth <david@...ntd.dyndns.org>,
linux-wireless <linux-wireless@...r.kernel.org>,
netdev@...r.kernel.org
Subject: Re: [PATCH/RFC] remove irqs_disabled warning from local_bh_enable
Ingo Molnar wrote:
> * Michael Buesch <mb@...sch.de> wrote:
>
>> On Friday 20 June 2008 18:01:09 Michael Buesch wrote:
>>> On Friday 20 June 2008 17:55:41 Ingo Molnar wrote:
>>>> * Michael Buesch <mb@...sch.de> wrote:
>>>>
>>>>> On Friday 20 June 2008 17:27:48 Ingo Molnar wrote:
>>>>>> [<c012b361>] local_bh_enable_ip+0xd1/0xe0
>>>>>> [<c08d9f9f>] _spin_unlock_bh+0x2f/0x40
>>>>>> [<c0471b92>] vortex_timer+0xe2/0x3e0
>>>>>> real bug or false positive?
>>>>> Well, a timer runs with IRQs disabled, no? So this would be a bug.
>>>> indeed - agreed :) [no time for me to fix it, but can test any rfc patch.]
>>> A quick workaround always is to convert the lock into an _irqsafe lock.
>>> Although it introduces higher overhead (interrupt-wise), it prevents the bug.
>>> A real fix would require to understand the locking in the driver, which I
>>> don't, as I never looked at the driver. :)
>>
>> However, looking at the driver I think the fix actually is trivial:
>>
>> Index: wireless-testing/drivers/net/3c59x.c
>> ===================================================================
>> --- wireless-testing.orig/drivers/net/3c59x.c 2008-05-16 00:26:29.000000000 +0200
>> +++ wireless-testing/drivers/net/3c59x.c 2008-06-20 18:16:55.000000000 +0200
>> @@ -1768,9 +1768,10 @@ vortex_timer(unsigned long data)
>> case XCVR_MII: case XCVR_NWAY:
>> {
>> ok = 1;
>> - spin_lock_bh(&vp->lock);
>> + /* Interrupts are already disabled */
>> + spin_lock(&vp->lock);
>> vortex_check_media(dev, 0);
>> - spin_unlock_bh(&vp->lock);
>> + spin_unlock(&vp->lock);
>> }
>> break;
>> default: /* Other media types handled by Tx timeouts. */
>>
>>
>> vp->lock is also taken in hardware IRQ context, so we _have_ to always
>> use irqsafe locking. As we run in a timer with IRQs disabled, we can
>> simply use spin_lock.
>
> thanks Michael! I have applied your fix to the tip/out-of-tree
> local/non-propagated fixlets branch for more testing. It takes up to 4
> hours to trigger this warning on that testbox, so i should know it
> whether it fixes the bug later today.
>
> Cc:-ed Jeff, he might want to pick up this fix, find the tidied up
> commit below. (3c59x is still present in various older laptops, so
> -stable candidate too i guess.)
>
> Ingo
>
> ---------------------->
> commit 24a5454d9f7863b00143760197f0ec29c8234289
> Author: Michael Buesch <mb@...sch.de>
> Date: Fri Jun 20 18:18:34 2008 +0200
>
> net, vortex: fix lockup
>
> Ingo Molnar reported:
>
> -tip testing found that Johannes Berg's "softirq: remove irqs_disabled
> warning from local_bh_enable" enhancement to lockdep triggers a new
> warning on an old testbox that uses 3c59x vortex and netlogging:
>
> ----->
> calling vortex_init+0x0/0xb0
> PCI: Found IRQ 10 for device 0000:00:0b.0
> PCI: Sharing IRQ 10 with 0000:00:0a.0
> PCI: Sharing IRQ 10 with 0000:00:0b.1
> 3c59x: Donald Becker and others.
> 0000:00:0b.0: 3Com PCI 3c556 Laptop Tornado at e0800400.
> PCI: Enabling bus mastering for device 0000:00:0b.0
> initcall vortex_init+0x0/0xb0 returned 0 after 47 msecs
> ...
> calling init_netconsole+0x0/0x1b0
> netconsole: local port 4444
> netconsole: local IP 10.0.1.9
> netconsole: interface eth0
> netconsole: remote port 4444
> netconsole: remote IP 10.0.1.16
> netconsole: remote ethernet address 00:19:xx:xx:xx:xx
> netconsole: device eth0 not up yet, forcing it
> eth0: setting half-duplex.
> eth0: setting full-duplex.
> ------------[ cut here ]------------
> WARNING: at kernel/softirq.c:137 local_bh_enable_ip+0xd1/0xe0()
> Pid: 1, comm: swapper Not tainted 2.6.26-rc6-tip #2091
> [<c0125ecf>] warn_on_slowpath+0x4f/0x70
> [<c0126834>] ? release_console_sem+0x1b4/0x1d0
> [<c0126d00>] ? vprintk+0x2a0/0x450
> [<c012fde5>] ? __mod_timer+0xa5/0xc0
> [<c046f7fd>] ? mdio_sync+0x3d/0x50
> [<c0160ef6>] ? marker_probe_cb+0x46/0xa0
> [<c0126ed7>] ? printk+0x27/0x50
> [<c046f4c3>] ? vortex_set_duplex+0x43/0xc0
> [<c046f521>] ? vortex_set_duplex+0xa1/0xc0
> [<c0471b92>] ? vortex_timer+0xe2/0x3e0
> [<c012b361>] local_bh_enable_ip+0xd1/0xe0
> [<c08d9f9f>] _spin_unlock_bh+0x2f/0x40
> [<c0471b92>] vortex_timer+0xe2/0x3e0
> [<c014743b>] ? trace_hardirqs_on+0xb/0x10
> [<c0147358>] ? trace_hardirqs_on_caller+0x88/0x160
> [<c012f8b2>] run_timer_softirq+0x162/0x1c0
> [<c0471ab0>] ? vortex_timer+0x0/0x3e0
> [<c012b361>] local_bh_enable_ip+0xd1/0xe0
> [<c08d9f9f>] _spin_unlock_bh+0x2f/0x40
> [<c0471b92>] vortex_timer+0xe2/0x3e0
> [<c014743b>] ? trace_hardirqs_on+0xb/0x10
> [<c0147358>] ? trace_hardirqs_on_caller+0x88/0x160
> [<c012f8b2>] run_timer_softirq+0x162/0x1c0
> [<c0471ab0>] ? vortex_timer+0x0/0x3e0
> [<c0471ab0>] ? vortex_timer+0x0/0x3e0
> [<c012b60a>] __do_softirq+0x9a/0x160
> [<c012b570>] ? __do_softirq+0x0/0x160
> [<c0106775>] call_on_stack+0x15/0x30
> [<c012b4f5>] ? irq_exit+0x55/0x60
> [<c0106e85>] ? do_IRQ+0x85/0xd0
> [<c0147391>] ? trace_hardirqs_on_caller+0xc1/0x160
> [<c0104888>] ? common_interrupt+0x28/0x30
> [<c08d8ac8>] ? mutex_unlock+0x8/0x10
> [<c08d8180>] ? _cond_resched+0x10/0x30
> [<c07a3be7>] ? netpoll_setup+0x117/0x390
> [<c0cbfcfe>] ? init_netconsole+0x14e/0x1b0
> [<c013d539>] ? ktime_get+0x19/0x40
> [<c0c9bab2>] ? kernel_init+0x1b2/0x2c0
> [<c0cbfbb0>] ? init_netconsole+0x0/0x1b0
> [<c0396aa4>] ? trace_hardirqs_on_thunk+0xc/0x10
> [<c0103f12>] ? restore_nocheck_notrace+0x0/0xe
> [<c0c9b900>] ? kernel_init+0x0/0x2c0
> [<c0c9b900>] ? kernel_init+0x0/0x2c0
> [<c0104aa7>] ? kernel_thread_helper+0x7/0x10
> =======================
> ---[ end trace 37f9c502aff112e0 ]---
> console [netcon0] enabled
> netconsole: network logging started
> initcall init_netconsole+0x0/0x1b0 returned 0 after 2914 msecs
>
> looking at the driver I think the bug is real and the fix actually
> is trivial.
>
> vp->lock is also taken in hardware IRQ context, so we _have_ to always
> use irqsafe locking. As we run in a timer with IRQs disabled,
> we can simply use spin_lock.
>
> Cc: <stable@...nel.org>
> Signed-off-by: Ingo Molnar <mingo@...e.hu>
>
> diff --git a/drivers/net/3c59x.c b/drivers/net/3c59x.c
> index 2edda8c..aabad8c 100644
> --- a/drivers/net/3c59x.c
> +++ b/drivers/net/3c59x.c
> @@ -1768,9 +1768,10 @@ vortex_timer(unsigned long data)
> case XCVR_MII: case XCVR_NWAY:
> {
> ok = 1;
> - spin_lock_bh(&vp->lock);
> + /* Interrupts are already disabled */
> + spin_lock(&vp->lock);
> vortex_check_media(dev, 0);
> - spin_unlock_bh(&vp->lock);
> + spin_unlock(&vp->lock);
applied
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