[GitHub] [trafficserver] maskit commented on issue #7562: Crash in HttpTunnel::consumer_reenable

[GitBox <gi...@apache.org>]

maskit commented on issue #7562:
URL: https://github.com/apache/trafficserver/issues/7562#issuecomment-786355180


   The crash happens if a producer is throttled (flow controlled) and background fill starts.
   Workaround is to disable flow control (`proxy.config.http.flow_control.enabled`).
   
   Here is the detail:
   
   `consumer_handler` calls `HttpSM::tunnel_handler_ua` here
   https://github.com/apache/trafficserver/blob/e24c79a4a530dc9b12880503e8c047e5610c3224/proxy/http/HttpTunnel.cc#L1317-L1330
   
   And if background fill starts in `HttpSM::tunnel_handler_ua`, a consumer for client is closed here.
   https://github.com/apache/trafficserver/blob/e24c79a4a530dc9b12880503e8c047e5610c3224/proxy/http/HttpSM.cc#L3326-L3329
   
   So the consumer `c` is no longer available at this point.
   
   However, this block somehow calls `consumer_reenable` for the consumer that has just been closed, despite the comment.
   https://github.com/apache/trafficserver/blob/e24c79a4a530dc9b12880503e8c047e5610c3224/proxy/http/HttpTunnel.cc#L1367-L1379
   
   `consumer_reenable` uses the consumer here and ATS crashes, because `write_vio` is null.
   https://github.com/apache/trafficserver/blob/e24c79a4a530dc9b12880503e8c047e5610c3224/proxy/http/HttpTunnel.cc#L1272-L1280
   
   The reenabling above won't happen if flow control is disabled, because throttling happens only if flow control is enabled.
   
   


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