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

* Michael Buesch <mb@bu3sch.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@bu3sch.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@bu3sch.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@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.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);
}
break;
default: /* Other media types handled by Tx timeouts. */

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