Messages in this thread | | | Date | Wed, 4 Jun 2014 10:16:12 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH 1/1] rtmutex: Handle when top lock owner changes |
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On Wed, 4 Jun 2014 08:05:25 -0500 "Brad Mouring" <bmouring@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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