On Thu, Jul 13, 2017 at 11:50:52AM +0200, Peter Zijlstra wrote:
> wait_for_completion(&C);
> atomic_inc_return();
>
> mutex_lock(A1);
> mutex_unlock(A1);
>
>
> <IRQ>
> spin_lock(B1);
> spin_unlock(B1);
>
> ...
>
> spin_lock(B64);
> spin_unlock(B64);
> </IRQ>
>
>
> mutex_lock(A2);
> mutex_unlock(A2);
>
> complete(&C);
>
>
> That gives:
>
> xhist[ 0] = A1
We have to rollback here later on irq_exit.
The followings are ones for irq context.
> xhist[ 1] = B1
> ...
> xhist[63] = B63
>
> then we wrap and have:
>
> xhist[0] = B64
>
> then we rewind to 1 and invalidate to arrive at:
>
Now, whether xhist[0] has been overwritten or not is important. If yes,
xhist[0] should be NULL, _not_ xhist[1], which is one for irq context so
not interest at all.
> xhist[ 0] = B64
> xhist[ 1] = NULL <-- idx
Therefore, it should be,
xhist[ 0] = NULL <- invalidate, cannot use it any more
--- <- on returning back from irq context, start from here
xhist[ 1] = B1 <-- obsolete history of irq
> xhist[ 2] = B2
> ...
> xhist[63] = B63
>
>
> Then we do A2 and get
>
> xhist[ 0] = B64
> xhist[ 1] = A2 <-- idx
> xhist[ 2] = B2
> ...
> xhist[63] = B63
So invalidating only one is enough.
