[dpdk-dev] [Bug 804] distributor: exiting workers can hang distributor core

[bugzilla@dpdk.org]

https://bugs.dpdk.org/show_bug.cgi?id=804

            Bug ID: 804
           Summary: distributor: exiting workers can hang distributor core
           Product: DPDK
           Version: 21.08
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: examples
          Assignee: dev@dpdk.org
          Reporter: brian90013@gmail.com
  Target Milestone: ---

Created attachment 171
  --> https://bugs.dpdk.org/attachment.cgi?id=171&action=edit
patch to avoid hanging

Hello,

I have been testing the distributor example using one interface and five cores
- ./build/distributor_app -l 10-14 -- -p 1. This leaves me one worker thread. I
noticed the application often hangs after I supply SIGINT and I have to
manually kill the process.

I added some additional debugging and discovered the distributor core is not
returning from rte_distributor_flush(). Looking inside that function, I see the
loop waiting for total_outstanding() to return 0. I believe that requires all
workers to have returned all in-flight packets?

Moving to the worker core, it calls rte_distributor_get_pkt(), does its
processing, then loops to the start of the while(!quit_signal_work) block. When
exiting, this is true, so it immediately exits the loop - without returning the
last batch of packets. I believe this is what is causing the distributor core
to fail to exit as it continues to loop waiting for workers to return their
buffers.

As a test, I added a call to rte_distributor_return_pkt(d, id, buf, num)
outside the worker while() loop but before the thread exits. I've run many
tests and have not seen the process hang once.

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