linux-kernel - [BUG] packet loss with PROVE_LOCKING, bisected to EDAC fix

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Message-ID: <20160321214209.GA8480@localhost>
Date:	Mon, 21 Mar 2016 21:42:09 +0000
From:	Chris Bainbridge <chris.bainbridge@...il.com>
To:	bp@...en8.de
Cc:	linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
	mchehab@...radead.org, markus@...ppelsdorf.de, tony.luck@...el.com
Subject: [BUG] packet loss with PROVE_LOCKING, bisected to EDAC fix

Hi,

I was testing something on an old server (Dell T105 opteron) and noticed
packet loss after updating the kernel from 3.10 to 4.5. The test was:

On Dell run: iperf -s
On another system: iperf3 -c dell -u -b 20M -l 1k -t 1000

This sends a 20mbit UDP stream to the Dell. It works fine normally (0%
packet loss), but when CONFIG_PROVE_LOCKING is enabled there is high
(35%) packet loss. (DEBUG_LOCKDEP also seems to cause packet loss)

The packet loss bisected back to:

commit 88d84ac97378c2f1d5fec9af1e8b7d9a662d6b00
Author: Borislav Petkov <bp@...e.de>
Date:   Fri Jul 19 12:28:25 2013 +0200

    EDAC: Fix lockdep splat

I have confirmed that the commit preceding this (v3.11-rc1) is fine and
that 88d84a introduced the bug.