netdev - Re: Is netif_tx_lock() SMP PREEMPT safe?

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Date:	Fri, 15 Feb 2008 17:01:03 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Marin Mitov <mitov@...p.bas.bg>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: Is netif_tx_lock() SMP PREEMPT safe?

Marin Mitov a écrit :
> Hi all,
>
> As in: include/linux/netdevice.h (kernel-2.6.24.2) one finds:
>
> static inline void __netif_tx_lock(struct net_device *dev, int cpu)
> {
>         spin_lock(&dev->_xmit_lock);
>         dev->xmit_lock_owner = cpu;
> }
>
> static inline void netif_tx_lock(struct net_device *dev)
> {
>         __netif_tx_lock(dev, smp_processor_id());
> }
>
> Does netif_tx_lock(struct net_device *dev) expands into:
>
> cpu = smp_processor_id(); 
> <preempt & shift to another cpu (bogus)>
> spin_lock(&dev->_xmit_lock);
> dev->xmit_lock_owner = cpu; /* cpu is not the lock owner */
>
> Or to:
>
> spin_lock(&dev->_xmit_lock);
> dev->xmit_lock_owner = smp_processor_id();
>
> which is correct?
>
>   
Hi Marin

This expands to the first version, but netif_tx_lock() is allways called 
with preemption disabled.

(Or checks in smp_processor_id() would just trigger)


Eric
(Cced netdev for network related stuff)





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