On Thursday 12/17 at 17:10 -0800, Stephen Hemminger wrote:

On Thu, 17 Dec 2015 15:52:39 -0800
Calvin Owens [off-list ref] wrote:

quoted

With built-in netconsole and IXGBE, configuring netconsole via the kernel
cmdline results in the following panic at boot:

    netpoll: netconsole: device eth0 not up yet, forcing it
    usb 2-1: new high-speed USB device number 2 using ehci-pci
    ixgbe 0000:03:00.0: registered PHC device on eth0
    BUG: unable to handle kernel NULL pointer dereference at 0000000000000810
    <snip>
    Call Trace:
     [<ffffffff81578661>] ? vxlan_get_rx_port+0x41/0xa0
     [<ffffffff81586828>] ixgbe_open+0x4e8/0x540
     [<ffffffff8168045c>] __dev_open+0xac/0x120
     [<ffffffff81680506>] dev_open+0x36/0x70
     [<ffffffff8169abec>] netpoll_setup+0x23c/0x300
     [<ffffffff8169a66a>] ? netpoll_parse_options+0x19a/0x200
     [<ffffffff81d797a8>] ? option_setup+0x1f/0x1f
     [<ffffffff81d79882>] init_netconsole+0xda/0x262
     [<ffffffff81d797a8>] ? option_setup+0x1f/0x1f
     [<ffffffff810003a8>] do_one_initcall+0x88/0x1b0
     [<ffffffff81d31144>] kernel_init_freeable+0x14a/0x1e3
     [<ffffffff81d308f1>] ? do_early_param+0x8c/0x8c
     [<ffffffff81778610>] ? rest_init+0x80/0x80
     [<ffffffff8177861e>] kernel_init+0xe/0xe0
     [<ffffffff8177dc5f>] ret_from_fork+0x3f/0x70
     [<ffffffff81778610>] ? rest_init+0x80/0x80

This happens because IXGBE assumes that vxlan has already been initialized.
The cleanest way to fix this is to just initialize netconsole after all the
other core networking stuff has completed.

Signed-off-by: Calvin Owens <redacted>

Fixing this by changing Makefile order is too fragile.
You are depending on the fact that Makefile order determines link order
and that determines initialization order. Down that path demons lie.

Hmm, include/linux/init.h explicitly states that "Ordering inside the
subsections is determined by link order", and has since before the
beginning of the history in Git.

I agree it seems magic/scary, but as Eric says I would imagine this
behavior is relied upon in other places.