[ofa-general] Re: [PATCHv3 for-2.6.21] IB/mthca: fix race in QP destroy

[Roland Dreier]

 > > I'm not quite sure I understand why we have to synchronize against the
 > > completion EQ's interrupt here.
 > 
 > Hmm, I'm not sure myself, now.
 > I'm still thinking about this - the patch below is clearly correct
 > and seems sufficient to fix the issue pointed out by bugzilla.
 > So let's get it merged and I'll try to think about and address
 > other isses (if any) in a separate patch.

The more I think about it, the more I think that synchronizing against
the completion interrupt doesn't accomplish anything.  The completion
interrupt itself only looks at the CQ, so it doesn't matter what we do
with the QP table or anything to do with QPs.  And a consumer could
poll any CQ at any time, in or out of interrupt context, so we're not
protecting against anything that has to do with polling CQs.

However, it does seem that we should also clean the CQs before
removing the QP from the table, to avoid polling completions for a QP
not in the QP table.  

And also synchronizing with the async event EQ's interrupts still
makes sense to me.

I guess I don't quite understand why this change is enough to fix bug
#394 -- it seems it is just changing the timing without really closing
the race window completely.

 - R.