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    Subject[PATCH] Re: forcedeth: lockdep warning on ethtool -s
    Andrew Morton wrote:
    > On Sun, 1 Jun 2008 10:37:01 +0200 Tobias Diedrich <ranma+kernel@tdiedrich.de> wrote:
    >
    > > Hi,
    > >
    > > After enabling CONFIG_LOCKDEP and CONFIG_PROVE_LOCKING I get the
    > > following warning when ethtool -s is first called on one of the
    > > forcedeth ports:
    > >
    > > =================================
    > > [ INFO: inconsistent lock state ]
    > > 2.6.26-rc4 #28
    > > ---------------------------------
    > > inconsistent {in-hardirq-W} -> {hardirq-on-W} usage.
    > > ethtool/1985 [HC0[0]:SC0[1]:HE1:SE0] takes:
    > > (&np->lock){++..}, at: [<ffffffffa000c5fd>] nv_set_settings+0xc8/0x3de [forcedeth]
    > > {in-hardirq-W} state was registered at:
    > > [<ffffffffffffffff>] 0xffffffffffffffff
    > > irq event stamp: 3606
    > > hardirqs last enabled at (3605): [<ffffffff8068106f>] _spin_unlock_irqrestore+0x3f/0x68
    > > hardirqs last disabled at (3604): [<ffffffff80680d38>] _spin_lock_irqsave+0x13/0x46
    > > softirqs last enabled at (3534): [<ffffffff80246ba5>] __do_softirq+0xbc/0xc5
    > > softirqs last disabled at (3606): [<ffffffff80680b33>] _spin_lock_bh+0x11/0x41
    > >
    > > other info that might help us debug this:
    > > 2 locks held by ethtool/1985:
    > > #0: (rtnl_mutex){--..}, at: [<ffffffff80596072>] rtnl_lock+0x12/0x14
    > > #1: (_xmit_ETHER){-+..}, at: [<ffffffffa000c5e8>] nv_set_settings+0xb3/0x3de [forcedeth]
    > >
    > > stack backtrace:
    > > Pid: 1985, comm: ethtool Not tainted 2.6.26-rc4 #28
    > >
    > > Call Trace:
    > > [<ffffffff8025f190>] print_usage_bug+0x162/0x173
    > > [<ffffffff8025fa8b>] mark_lock+0x231/0x41f
    > > [<ffffffff802607cf>] __lock_acquire+0x4e7/0xcac
    > > [<ffffffff8025fe64>] ? trace_hardirqs_on+0xf1/0x115
    > > [<ffffffff80272c3a>] ? disable_irq_nosync+0x6f/0x7b
    > > [<ffffffff80261375>] lock_acquire+0x55/0x6e
    > > [<ffffffffa000c5fd>] ? :forcedeth:nv_set_settings+0xc8/0x3de
    > > [<ffffffff80680b15>] _spin_lock+0x2f/0x3c
    > > [<ffffffffa000c5fd>] :forcedeth:nv_set_settings+0xc8/0x3de
    > > [<ffffffff8058f8bb>] dev_ethtool+0x186/0xea3
    > > [<ffffffff8067f446>] ? mutex_lock_nested+0x243/0x275
    > > [<ffffffff8025df2b>] ? debug_mutex_free_waiter+0x46/0x4a
    > > [<ffffffff8067f469>] ? mutex_lock_nested+0x266/0x275
    > > [<ffffffff8058e1ce>] dev_ioctl+0x4eb/0x600
    > > [<ffffffff8068106f>] ? _spin_unlock_irqrestore+0x3f/0x68
    > > [<ffffffff80580f91>] sock_ioctl+0x1f5/0x202
    > > [<ffffffff802a322e>] vfs_ioctl+0x2a/0x77
    > > [<ffffffff802a34d6>] do_vfs_ioctl+0x25b/0x270
    > > [<ffffffff806807b6>] ? trace_hardirqs_on_thunk+0x35/0x3a
    > > [<ffffffff802a352d>] sys_ioctl+0x42/0x65
    > > [<ffffffff8021fffb>] system_call_after_swapgs+0x7b/0x80
    > >
    > >
    > > I think this is caused by the following snippet in nv_set_settings:
    > >
    > > netif_carrier_off(dev);
    > > if (netif_running(dev)) {
    > > nv_disable_irq(dev);
    > > netif_tx_lock_bh(dev);
    > > spin_lock(&np->lock);
    > > /* stop engines */
    > > nv_stop_rxtx(dev);
    > > spin_unlock(&np->lock);
    > > netif_tx_unlock_bh(dev);
    > > }
    > >
    > >
    > > Because of nv_disable_irq this is probably not really a problem
    > > though (I guess) and replacing the spin_lock with spin_lock_irqsave
    > > could keep interrupts disabled for a longer period of time because
    > > of delays in nv_stop_rx and nv_stop_tx.
    >
    > Could you please try that and if it works, send the patch?

    Here you go, with this patch applied I get no warning:

    Signed-Off-By: Tobias Diedrich <ranma+kernel@tdiedrich.de>

    Index: linux-2.6.26-rc4.forcedwol/drivers/net/forcedeth.c
    ===================================================================
    --- linux-2.6.26-rc4.forcedwol.orig/drivers/net/forcedeth.c 2008-06-15 20:45:32.000000000 +0200
    +++ linux-2.6.26-rc4.forcedwol/drivers/net/forcedeth.c 2008-06-15 20:55:27.000000000 +0200
    @@ -4198,12 +4198,23 @@

    netif_carrier_off(dev);
    if (netif_running(dev)) {
    + unsigned long flags;
    +
    nv_disable_irq(dev);
    netif_tx_lock_bh(dev);
    - spin_lock(&np->lock);
    + /* with plain spinlock lockdep complains */
    + spin_lock_irqsave(&np->lock, flags);
    /* stop engines */
    + /* FIXME:
    + * this can take some time, and interrupts are disabled
    + * due to spin_lock_irqsave, but let's hope no daemon
    + * is going to change the settings very often...
    + * Worst case:
    + * NV_RXSTOP_DELAY1MAX + NV_TXSTOP_DELAY1MAX
    + * + some minor delays, which is up to a second approximately
    + */
    nv_stop_rxtx(dev);
    - spin_unlock(&np->lock);
    + spin_unlock_irqrestore(&np->lock, flags);
    netif_tx_unlock_bh(dev);
    }

    --
    Tobias PGP: http://9ac7e0bc.uguu.de
    このメールは十割再利用されたビットで作られています。
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