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    SubjectRe: [PATCH/RFC] remove irqs_disabled warning from local_bh_enable
    Ingo Molnar wrote:
    > * 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);

    applied




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