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From: Marin Mitov <mitov@issp.bas.bg>
To: linux-kernel@vger.kernel.org
Subject: Is netif_tx_lock() SMP PREEMPT safe?
Date: Fri, 15 Feb 2008 17:25:05 +0200
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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?

Thanks in advance for your answer.

Regards

Marin Mitov