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Date: Tue, 30 Nov 2010 01:23:12 +0600
From: Eugene Grosbein <eugen@eg.sd.rdtc.ru>
To: Jack Vogel <jfvogel@gmail.com>
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Cc: freebsd-net <freebsd-net@freebsd.org>,
	Eugene Grosbein <eugen@eg.sd.rdtc.ru>
Subject: Re: em(4) updated to version 7.1.8
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On Mon, Nov 29, 2010 at 11:10:22AM -0800, Jack Vogel wrote:

> Not sure what code you created this from, but its not the new driver,

Yes, that's for previous version and that's what keeps my production
servers from panicing.

> things have been reorganized and I do not believe this issue exists.
> Please test with the latest.

I'd rather not risk. Here is the same check for today's RELENG_8 driver.
Please, please take a look. After several days of nearly gigabit load
it has already happened m_head was NULL here, in previous version.
Can it be possible in current version?
There is still no check before dereferencing.

--- if_em.c.orig	2010-11-30 01:16:17.000000000 +0600
+++ if_em.c	2010-11-30 01:19:09.000000000 +0600
@@ -4321,10 +4321,12 @@
                          
 	/* Reset state, keep loaded DMA map and reuse */
 	m = rbuf->m_head;
+	if(m) {
 	m->m_len = m->m_pkthdr.len = adapter->rx_mbuf_sz;
 	m->m_flags |= M_PKTHDR;
 	m->m_data = m->m_ext.ext_buf;
 	m->m_next = NULL;
+	}
 
 	return;
 }