On Fri, Jul 14, 2017 at 03:42:10PM +0900, Byungchul Park wrote:
> On Thu, Jul 13, 2017 at 08:23:33PM +0900, Byungchul Park wrote:
> > On Thu, Jul 13, 2017 at 8:12 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > > On Thu, Jul 13, 2017 at 12:29:05PM +0200, Peter Zijlstra wrote:
> > >> On Thu, Jul 13, 2017 at 07:09:53PM +0900, Byungchul Park wrote:
> > >> > 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>
> > >> > >
> > >> > >
> > >
> > > Also consider the alternative:
> > >
> > > <IRQ>
> > > spin_lock(D);
> > > spin_unlock(D);
> > >
> > > complete(&C);
> > > </IRQ>
> > >
> > > in which case the context test will also not work.
> >
> > Context tests are done on xhlock with the release context, _not_
> > acquisition context. For example, spin_lock(D) and complete(&C) are
> > in the same context, so the test would pass in this example.
The point was, this example will also link C to B*.
(/me copy paste from older email)
That gives:
xhist[ 0] = A1
xhist[ 1] = B1
...
xhist[63] = B63
then we wrap and have:
xhist[0] = B64
then we rewind to 1 and invalidate to arrive at:
xhist[ 0] = B64
xhist[ 1] = NULL <-- idx
xhist[ 2] = B2
...
xhist[63] = B63
Then we do D and get
xhist[ 0] = B64
xhist[ 1] = D <-- idx
xhist[ 2] = B2
...
xhist[63] = B63
And now there is nothing that will invalidate B*, after all, the
gen_id's are all after C's stamp, and the same_context_xhlock() test
will also pass because they're all from IRQ context (albeit not the
same, but it cannot tell).
Does this explain? Or am I still missing something?
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