On Tue, 2006-05-30 at 11:14 +0200, Benoit Boissinot wrote:
> On 5/29/06, Ingo Molnar <[email protected]> wrote:
> > We are pleased to announce the first release of the "lock dependency
> > correctness validator" kernel debugging feature, which can be downloaded
> > from:
> >
> > http://redhat.com/~mingo/lockdep-patches/
> > [snip]
>
> I get this right after ipw2200 is loaded (it is quite verbose, I
> probably shoudln't post everything...)
>
> ipw2200: Detected Intel PRO/Wireless 2200BG Network Connection
> ipw2200: Detected geography ZZD (13 802.11bg channels, 0 802.11a channels)
> <c0301efa> netlink_broadcast+0x7a/0x360
this isn't allow to be called from IRQ context, because it takes
nl_table_lock for read, but that is taken as
write_lock_bh(&nl_table_lock);
in
static void netlink_table_grab(void)
so without disabling interrupts; which would thus deadlock if this
read_lock-from-irq would hit.
> <c02fb6a4> wireless_send_event+0x304/0x340
> <e1cf8e11> ipw_rx+0x1371/0x1bb0 [ipw2200]
> <e1cfe6ac> ipw_irq_tasklet+0x13c/0x500 [ipw2200]
> <c0121ea0> tasklet_action+0x40/0x90
but it's more complex than that, since we ARE in BH context.
The complexity comes from us holding &priv->lock, which is
used in hard irq context.
so the deadlock is like this:
cpu 0: user context cpu1: softirq context
netlink_table_grab takes nl_table_lock as take priv->lock in ipw_irq_tasklet
write_lock_bh, but leaves irqs enabled
hardirq comes in and the isr tries to take in ipw_rx, call wireless_send_event which
priv->lock but has to wait on cpu 1 tries to take nl_table_lock for read
but has to wait for cpu0
and... kaboom kabang deadlock :)
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