Re: tun: Use netif_receive_skb instead of netif_rx

Eric Dumazet
2010-05-19T08:27:21Z

Le mercredi 19 mai 2010 à 18:20 +1000, Herbert Xu a écrit :
> On Wed, May 19, 2010 at 10:09:42AM +0200, Eric Dumazet wrote:
> >
> > 6) netif_rx() pro is that packet processing is done while stack usage is
> > guaranteed to be low (from process_backlog, using a special softirq
> > stack, instead of current stack)
> >
> > After your patch, tun will use more stack. Is it safe on all contexts ?
>
> Dave also raised this but I believe nothing changes with regards
> to the stack. We currently call do_softirq which does not switch
> stacks.
>
> Only a real interrupt would switch stacks.

This is a bit wrong, at least here (CONFIG_4KSTACKS=y)

Some people still use 32bits these days ;)

Please check arch/x86/kernel/irq_32.c

asmlinkage void do_softirq(void)
{
unsigned long flags;
struct thread_info *curctx;
union irq_ctx *irqctx;
u32 *isp;

if (in_interrupt())
return;

local_irq_save(flags);

if (local_softirq_pending()) {
curctx = current_thread_info();
irqctx = __get_cpu_var(softirq_ctx);
irqctx->tinfo.task = curctx->task;
irqctx->tinfo.previous_esp = current_stack_pointer;

/* build the stack frame on the softirq stack */
isp = (u32 *) ((char *)irqctx + sizeof(*irqctx));

call_on_stack(__do_softirq, isp);
/*
* Shouldnt happen, we returned above if in_interrupt():
*/
WARN_ON_ONCE(softirq_count());
}

local_irq_restore(flags);
}