Re: [PATCH 1/4] Blackfin: arch patch for 2.6.18

Arnd Bergmann
2006-09-25T17:05:45Z

On Monday 25 September 2006 17:39, Aubrey wrote:
> 1) Timer interrupt will call do_irq(), then return_from_int().
>
> 2) return_from_int() will check if there is interrupt pending or
> signal pending, if so, it will call schedule_and_signal_from_int().
>
> 3) schedule_and_signal_from_int() will jump to resume_userspace()
>
> 4) resume_userspace() will call _schedule to run the user task.

I have a little trouble reading your assembly code, but your
return_from_int() function should normally not call
schedule_and_signal_from_int() when the interrupt happened
in kernel context (like in the idle function):

+ /* if not return to user mode, get out */
+ p2.l = lo(IPEND);
+ p2.h = hi(IPEND);
+ r0 = [p2];
+ r1 = 0x17(Z);
+ r2 = ~r1;
+ r2.h = 0;
+ r0 = r2 & r0;
+ r1 = 1;
+ r1 = r0 - r1;
+ r2 = r0 & r1;
+ cc = r2 == 0;
+ if !cc jump 2f;

This looks a lot like you user_mode() function, so you jump
over schedule_and_signal_from_int() here.

What you described would be a preemptive kernel
(CONFIG_PREEMPT), but you clearly don't have that enabled.