Re: 2.6.23-rc5: possible irq lock inversion dependency detected

[Herbert Xu]

On Sun, Sep 02, 2007 at 01:11:29PM +0000, Christian Kujau wrote:
> 
> after upgrading to 2.6.23-rc5 (and applying davem's fix [0]), lockdep 
> was quite noisy when I tried to shape my external (wireless) interface:
> 
> [ 6400.534545] FahCore_78.exe/3552 just changed the state of lock:
> [ 6400.534713]  (&dev->ingress_lock){-+..}, at: [<c038d595>] 
> netif_receive_skb+0x2d5/0x3c0
> [ 6400.534941] but this lock took another, soft-read-irq-unsafe lock in the 
> past:
> [ 6400.535145]  (police_lock){-.--}

This is a genuine dead-lock.  The police lock can be taken
for reading with softirqs on.  If a second CPU tries to take
the police lock for writing, while holding the ingress lock,
then a softirq on the first CPU can dead-lock when it tries
to get the ingress lock.

The minimal fix would be to make sure that we disable BH on
the first CPU.  Jamal, could you take a look at this please?

Thanks,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@xxxxxxxxxxxxxxxxxxx>
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