Re: [Adeos-main] Stall bit setting in __ipipe_handle_exception

[Jan Kiszka <jan.kiszka@domain.hid>]

Jan Kiszka wrote:
> Hi Philippe,
> 
> as already indicated, I'm starting to understand the ipipe bug Roman
> sees. It seems to melt down to the following path:
> 
> - exception raised over non-root domain (__rt_event_wait...)
> - root domain is stalled on entry of __ipipe_handle_exception
> - fault causing task is first relaxed, then scheduled away under Linux
> - scheduled-in Linux task was interrupted in __ipipe_divert_exception,
>   shortly before __fixup_if
> - __fixup_if finds root domain stalled and propagates this to the
>   register set of the interrupted context (user space task running on
>   its first fpu instruction, having triggered device_not_available).
> - return to user space task with irqs disable - bang!
> 
> Two ways to approach this:
> 1. Do we actually have to stall the root domain in
>    __ipipe_handle_exception before ipipe_trap_notify? I don't see why we
>    should be better off with doing this afterwards.

...why we should *not* be better off...

> 2. Avoid that __ipipe_divert_exception is interruptible and can pick up
>    the stall flag from a different Linux task. But I don't know if there
>    aren't more race windows like that.
> 
> Jan
> 

Jan

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