Re: [Xen-devel] do_softirq + interrupts

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 2 Sep 2005, at 00:14, Hollis Blanchard wrote:

> What confuses me is that any other interrupt could come in at point 
> *** above,
> right? That interrupt will follow a very similar path, calling 
> do_softirq
> again, and handle TIMER_SOFTIRQ. Then when the first do_softirq 
> resumes, the
> ASSERT will trip.
>
> What am I missing?
You shouldn't call do_softirq() from nested Xen activations (this is 
unlike Linux, which is happy to do softirq work from arbitrary 
interrupt contexts).
For example, the main places where arch/x86 calls do_softirq are from 
within the idle loop, and in our code that exits a Xen activation we 
have code along the lines of:
 if (softirq_pending() and returning to guest context) do_softirq();

If you do softirq work in nested interrupt contexts in Xen you will 
find all kinds of bad races, because the locking strategies assume you 
don;t do this (most spinlocks are acquired without disabling 
interrupts, for example).
 -- Keir




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel