[netdrvr] 3c59x: remove irqs_disabled warning from local_bh_enable

Original Author: Michael Buesch <mb@bu3sch.de>

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>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>