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Re: [PATCH/RFC] remove irqs_disabled warning from local_bh_enable

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* Michael Buesch <mb@xxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxx>
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@xxxxxxxxxx>
    Signed-off-by: Ingo Molnar <mingo@xxxxxxx>

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);
 		}
 		break;
 	  default:					/* Other media types handled by Tx timeouts. */
--
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