On Wed, 4 Jun 2014 08:05:25 -0500
"Brad Mouring" <bmour...@ni.com> wrote:
> A->L2
>
> This is a slight variation on what I was seeing. To use the nomenclature
> that you proposed at the start, rewinding to the point
>
> A->L2->B->L3->C->L4->D
>
> Let's assume things continue to unfold as you explain. Task is D,
> top_waiter is C. A is scheduled out and the chain shuffles.
>
> A->L2->B
> C->L4->D->'
But isn't that a lock ordering problem there?
If B can block on L3 owned by C, I see the following:
B->L3->C->L4->D->L2->B
Deadlock!
In my scenario I was very careful to point out that the lock ordering
was: L1->L2->L3->L4
But you show that we can have both:
L2-> ... ->L4
and
L4-> ... ->L2
Which is a reverse of lock ordering and a possible deadlock can occur.
-- Steve
>
> So, we now have D blocking on L2 and L4 has waiters, C again. Also,
> since the codepath to have C block on L4 again is the same as the
> codepath from when it blocked on it in the first place, the location
> is the same since the stack (for what we care about) is the same.
>
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