[tor-bugs] #24668 [Core Tor/Tor]: sched: scheduler_compare_channels() function will never pick a channel with no active circuis.

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#24668: sched: scheduler_compare_channels() function will never pick a channel with
no active circuis.
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 Reporter:  dgoulet                           |          Owner:  (none)
     Type:  defect                            |         Status:  new
 Priority:  Medium                            |      Milestone:  Tor:
                                              |  0.3.3.x-final
Component:  Core Tor/Tor                      |        Version:
 Severity:  Normal                            |     Resolution:
 Keywords:  tor-sched, tor-channel, tor-cell  |  Actual Points:
Parent ID:                                    |         Points:
 Reviewer:                                    |        Sponsor:
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Comment (by arma):

 Replying to [ticket:24668 dgoulet]:
 > To fix this one, we probably have to fix ewma_cmp_cmux() to look at
 destroy cells too (somehow).

 Yes, agreed.

 I assume this bug was introduced by our destroy cell queue fix from #7912
 (when we separated queued destroy cells from queued other-types-of-cells).

 How hard would it be to add the circuit to the active_circuit_pqueue when
 it has a non-empty destroy queue? Then it would at least get a chance to
 be considered, even if we aren't load balancing in an optimal way
 (whatever that means) between sending data cells and destroy cells.

 Looking more at #7912, it seems like we think we already did this. So
 maybe there is some simple bug somewhere in the current code where it
 doesn't get triggered correctly, rather than a fundamentally broken
 design?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24668#comment:1>
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