[GitHub] [trafficserver] sudheerv commented on issue #7096: Crash due to bug in Thread Context migration

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

sudheerv commented on issue #7096:
URL: https://github.com/apache/trafficserver/issues/7096#issuecomment-707689651


   After over 2 months of debugging, finally found the root cause of the issue. The issue is mainly caused by changing the (read) mutex from the server before acquiring from and releasing to the pool. The net i/o read (including EOS) is meant to be synchronized with the read vio mutex (which is the session pool mutex before acquiring from the pool and the HttpTunnel’s mutex before releasing to the pool) but in the process of disabling the i/o, the mutex is changed by calling do_io_read() with null continuation. This lets in a net read and also makes the “closed” flag checking unreliable in the net_read_io() corrupting the ssl or other heap memory. 
   
   Reproduced the behavior by tweaking the mutex windows and tested a fix that by tightening the windows and ensuring the mutex is preserved while the session acquire/release process is completed. 
   
   These issues are mostly specific to using global session sharing and for some reason having a lot of transform plugins acting on the server vc, seems to expose the race condition more. 
   
   In the process of debugging this, added a couple of mechanisms that helped - 
   1) tracking a VC event/callback history much like the SM history
   2) ssl -> vc book keeping to catch and prevent double deletes (this has caught a couple of bugs doing double deletes)


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