Re: FreeBSD 10-RC4: Got crash in igb driver

  Yonghyeon,

On Fri, Jan 10, 2014 at 10:21:14AM +0900, Yonghyeon PYUN wrote:
Y> > I experience some troubles with the igb device driver on FreeBSD 10-RC4.
Y> > 
Y> > The kernel make a pagefault in the igb_tx_ctx_setup function when accessing to 
Y> > a IPv6 header.
Y> > 
Y> > The network configuration is the following:
Y> >  - box acting as an IPv6 router
Y> >  - one interface with an IPv6 (igb0)
Y> >  - another interface with a vlan, and IPv6 on it (vlan0 on igb1)
Y> > 
Y> > Vlan Hardware tagging is set on both interfaces.
Y> > 
Y> > The packet that cause the crash come from igb0 and go to vlan0.
Y> > 
Y> > After investigation, i see that the mbuf is split in two. The first one carry 
Y> > the ethernet header, the second, the IPv6 header and data payload.
Y> > 
Y> > The split is due to the "m_copy" done in ip6_forward, that make the mbuf not 
Y> > writable and the "M_PREPEND" in ether_output that insert the new mbuf before 
Y> > the original one.
Y> > 
Y> > The kernel crashes only if the newly allocated mbuf is at the end of a memory 
Y> > page, and no page is available after this one. So, it's extremly rare.
Y> > 
Y> > I inserted a "KASSERT" into the function (see attached patch) to check this 
Y> > behavior, and it raises on every IPv6 forwarded packet to the vlan. The 
Y> > problem disapear if i remove hardware tagging.
Y> > 
Y> > In the commit 256200, i see that pullups has been removed. May it be related ?
Y> 
Y> I think I introduced the header parsing code to meet controller
Y> requirement in em(4) and Jack borrowed that code in the past but it
Y> seems it was removed in r256200.  It seems igb_tx_ctx_setup()
Y> assumes it can access ethernet/IP/TCP/UDP headers in the first mbuf
Y> of the chain.
Y> This looks wrong to me.

Can you please restore the important code in head ASAP? Although crashes happen
only when the mbuf is last in a page and page isn't mapped, we read thrash from
next allocation on almost every packet.

-- 
Totus tuus, Glebius.