From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.xen@gmail.com>
Subject: Re: [question] will softirq handler potentially be
 called many times?
Date: Fri, 17 Feb 2012 09:20:03 +0000
Message-ID: <CB63CC43.2B6E0%keir.xen@gmail.com>
References: <CANqQZNHc11vDEbkT2_JMER7FWeqdSQi+5_n1gN36BnJGs8mDiA@mail.gmail.com>
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On 17/02/2012 04:47, "Kai Huang" <mail.kai.huang@gmail.com> wrote:

> Hi,
> 
> I see the __do_softirq is called when ! in_atomic(), which means
> potentially __do_softirq may be interrupted by trap, exception,
> interrupt, etc, so seems softirq handler may be executed many times?
> 
> For example, if interrupt happens after i =
> find_first_set_bit(pending), the same softirq hander will be called
> twice as the do_softriq will be called after all interrupt handler
> returned, and the pending bit has not been cleared yet when first
> do_softirq was called.

Can't happen, we only call do_softirq() when returning from an interrupt
back to guest context. Therefore a nested interrupt call does not cause
do_softirq to run.

  -- Keir

> static void __do_softirq(unsigned long ignore_mask)
> {
>     ......
>     for ( ; ; )
>     {
>         ......
>         i = find_first_set_bit(pending);
>                                                    <- interrupt happens
>         clear_bit(i, &softirq_pending(cpu));
>         (*softirq_handlers[i])();
>     }
> }
> 
> -cody
> 
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