At boot, all attempts to open /dev/console failed.  dmesg shows:

Warning: unable to open an initial console.

from init/main.c:

        if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
                printk(KERN_WARNING "Warning: unable to open an initial console.\n");

problem originally hit in -mmotm, traced down to linux-next.
git bisect of linux-next find this:

31f8326f981117fc548d292656fa8dbed28bc42b is first bad commit
commit 31f8326f981117fc548d292656fa8dbed28bc42b
Author: Alan Cox <alan@lxorguk.ukuu.org.uk>
Date:   Thu Mar 12 10:00:15 2009 +1100

    tty-fix-mismatch-in-lookup-han
    
    The lookup methods return NULL or a pointer. The caller expects an ERR_PTR.
    It seems to make sense to just use NULL and return -ENODEV here as it keeps
    the code simple and clean and the way it always used to work (effectively)
    before the restructure
    
    Problem noticed by Jiri Slaby.
    
    Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>

:040000 040000 e6b1ddf54e63b5b7be2bfa07c6a21a9657e91d27 1ef01e18f00a713c3a0299725c6b594da5fcffbe M      drivers

Reverting this one commit made things start working again.  I admit not
understanding why this commit broke the sys_open().