Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> writes:
> The preempt_disable() () section was introduced in commit
> cece1945bffcf ("net: disable preemption before call smp_processor_id()")
>
> and adds it in case this function is invoked from preemtible context and
> because get_cpu() later on as been added.
>
> The get_cpu() usage was added in commit
> b0e28f1effd1d ("net: netif_rx() must disable preemption")
>
> because ip_dev_loopback_xmit() invoked netif_rx() with enabled preemption
> causing a warning in smp_processor_id(). The function netif_rx() should
> only be invoked from an interrupt context which implies disabled
> preemption. The commit
> e30b38c298b55 ("ip: Fix ip_dev_loopback_xmit()")
>
> was addressing this and replaced netif_rx() with in netif_rx_ni() in
> ip_dev_loopback_xmit().
>
> Based on the discussion on the list, the former patch (b0e28f1effd1d)
> should not have been applied only the latter (e30b38c298b55).
>
> Remove get_cpu() and preempt_disable() since the function is supposed to
> be invoked from context with stable per-CPU pointers. Bottom halves have
> to be disabled at this point because the function may raise softirqs
> which need to be processed.
>
> Link: https://lkml.kernel.org/r/20100415.013347.98375530.davem@xxxxxxxxxxxxx
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
