[tor-bugs] #21312 [Obfuscation/Snowflake]: snowflake-client is pegged at 100% cpu

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#21312: snowflake-client is pegged at 100% cpu
-----------------------------------+---------------------
 Reporter:  arlolra                |          Owner:
     Type:  defect                 |         Status:  new
 Priority:  Medium                 |      Milestone:
Component:  Obfuscation/Snowflake  |        Version:
 Severity:  Normal                 |     Resolution:
 Keywords:                         |  Actual Points:
Parent ID:                         |         Points:
 Reviewer:                         |        Sponsor:
-----------------------------------+---------------------

Comment (by dcf):

 I encountered this lockup for the first time today. snowflake-client was
 using 200% CPU. I had been browsing and my requests started timing out.
 Here is the end of snowflake.log; it must have been around 17:00:00 when I
 noticed the hang.
 {{{
 2017/08/09 16:58:43 ---- Handler: snowflake assigned ----
 2017/08/09 16:58:43 Buffered 201 bytes --> WebRTC
 2017/08/09 16:58:43 WebRTC: DataChannel.OnOpen
 2017/08/09 16:58:43 Flushed 201 bytes.
 2017/08/09 16:58:45 Traffic Bytes (in|out): 743 | 201 -- (1 OnMessages, 1
 Sends)
 2017/08/09 16:58:51 Traffic Bytes (in|out): 51 | 166 -- (1 OnMessages, 2
 Sends)
 2017/08/09 16:58:53 WebRTC: At capacity [1/1]  Retrying in 10 seconds...
 2017/08/09 16:59:03 WebRTC: At capacity [1/1]  Retrying in 10 seconds...
 2017/08/09 16:59:13 WebRTC: At capacity [1/1]  Retrying in 10 seconds...
 2017/08/09 16:59:17 WebRTC: No messages received for 30 seconds -- closing
 stale connection.
 2017/08/09 16:59:17 WebRTC: closing DataChannel
 2017/08/09 16:59:23 WebRTC: Collecting a new Snowflake. Currently at [0/1]
 2017/08/09 16:59:23 snowflake-SeQZtvutAUlE6pFr  connecting...
 2017/08/09 17:03:45 copy loop ended
 2017/08/09 17:03:45 ---- Handler: closed ---
 2017/08/09 17:03:45 SOCKS listening...
 2017/08/09 17:03:46 SOCKS accepted:  {0.0.3.0:1  map[]}
 }}}

 The process had 521 threads, not 1024.
  * [attachment:20170809-info-threads.txt info threads]
  * [attachment:20170809-thread-apply-all-bt.txt thread apply all bt]

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21312#comment:9>
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