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From: Ben Greear <>
To: netdev <>
Subject: Debugging stuck tcp connection across localhost
Date: Thu, 6 Jan 2022 06:59:58 -0800	[thread overview]
Message-ID: <> (raw)


I'm working on a strange problem, and could use some help if anyone has ideas.

On a heavily loaded system (500+ wifi station devices, VRF device per 'real' netdev,
traffic generation on the netdevs, etc), I see cases where two processes trying
to communicate across localhost with TCP seem to get a stuck network

[greearb@bendt7 ben_debug]$ grep 4004 netstat.txt |grep
tcp        0 7988926         ESTABLISHED
tcp        0  59805          ESTABLISHED

Both processes in question continue to execute, and as far as I can tell, they are properly
attempting to read/write the socket, but they are reading/writing 0 bytes (these sockets
are non blocking).  If one was stuck not reading, I would expect netstat
to show bytes in the rcv buffer, but it is zero as you can see above.

Kernel is 5.15.7+ local hacks.  I can only reproduce this in a big messy complicated
test case, with my local ath10k-ct and other patches that enable virtual wifi stations,
but my code can grab logs at time it sees the problem.  Is there anything
more I can do to figure out why the TCP connection appears to be stuck?


Ben Greear <>
Candela Technologies Inc

             reply	other threads:[~2022-01-06 15:06 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-06 14:59 Ben Greear [this message]
2022-01-06 15:20 ` Neal Cardwell
2022-01-06 15:39   ` Ben Greear
2022-01-06 16:16     ` Neal Cardwell
2022-01-06 19:05       ` Ben Greear
2022-01-06 20:04         ` Neal Cardwell
2022-01-06 20:20           ` Ben Greear
2022-01-06 22:26           ` Ben Greear
2022-01-10 18:10             ` Ben Greear
2022-01-10 22:16               ` David Laight
2022-01-11 10:46               ` Eric Dumazet
2022-01-11 21:35                 ` Ben Greear
2022-01-12  7:41                   ` Eric Dumazet
2022-01-12 14:52                     ` Ben Greear
2022-01-12 17:12                       ` Eric Dumazet
2022-01-12 18:01                         ` Debugging stuck tcp connection across localhost [snip] Ben Greear
2022-01-12 18:44                           ` Ben Greear
2022-01-12 18:47                             ` Eric Dumazet
2022-01-12 18:54                               ` Ben Greear

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