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[lwip-devel] [bug #42633] Write many frames at high speed to a PC stops

From: Sergio R. Caprile
Subject: [lwip-devel] [bug #42633] Write many frames at high speed to a PC stops communication random.
Date: Mon, 30 Jun 2014 13:14:26 +0000
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:30.0) Gecko/20100101 Firefox/30.0

Follow-up Comment #5, bug #42633 (project lwip):

the capture snapshot clearly shows that you are missing a segment somewhere,
there is a big sign in wireshark telling you that, and the PC does not ACK
what you sent because it is missing what you did NOT send, and THAT is the
missing segment.
frame 13888: "TCP previous segment not captured"
frame 13887: your seq is 2969 and you send 1360 bytes, then the next segment
(frame 13888) has seq 7049
7049 - 1360 - 2969 = 2720 = 2*1360 bytes missing "somewhere" in between your
function call to send and the PC + wireshark. This looks like a memory
problem, however, I'm no expert here.
frame 13892, and all the others in black saying "dup ACK": The PC is sending
ACK to 4329 telling the sender to send that, what you didn't.
This is the magic of networking.
I don't know why there is a segment missing, if frames got lost in DMA, TCP
should still have them, or is there a no copy option that causes TCP to lose
what it has sent before it gets an ACK ? Is there any way of "bad calling" the
stack to cause it to skip a segment ?
I think this is memory corruption caused by reentrancy.


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