[Varnish] #783: Critbit crash in Varnish 2.1.3

[Varnish]

#783: Critbit crash in Varnish 2.1.3
----------------------+-----------------------------------------------------
 Reporter:  anders    |        Owner:  phk   
     Type:  defect    |       Status:  closed
 Priority:  normal    |    Milestone:        
Component:  varnishd  |      Version:  2.1.3 
 Severity:  major     |   Resolution:  fixed 
 Keywords:            |  
----------------------+-----------------------------------------------------

Comment(by tfheen):

 (In [5368]) Merge r5304: Remove bogus assert

 After considerable thinking, I have come to the conclusion that this
 assert is bogus.

 There is a window from our lookup until we lock the refcount where
 a different thread conceiveably could loose the last reference to
 the objhdr, before we get the lock to increase it.

 The situation the assert was meant to protect, where we insert
 a new objhdr, is handled in the "oh == noh" clause earlier, were
 the weaker "> 0" check is used (rather than "== 1") to cater for
 the exact same race.

 Fixes: #761
 Fixes: #783

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Ticket URL: </ticket/783#comment:3>
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