3.7-rc6 soft lockup in kswapd0

["George Spelvin" <linux@horizon.com>]

I'm having an interesting issue with a uniprocessor Pentium 4 machine
locking up overnight.  3.6.5 didn't do that, but 3.7-rc6 is not doing
so well.

It's kind of a funny lockup.  Some things work:

- TCP SYN handshake
- Alt-SysRq

And others don't:

- Caps lock
- Shift-PgUp
- Alt-Fn
- Screen unblanking
- Actually talking to a daemon

This is a "headless" machine that boots to a text console and has zero
console activity until the lockup.

This has happened overnight, three nights in a row.  I had to turn screen
blanking off to see anything on the screen.  Running the daily cron jobs
manually just now didn't trigger it, so I haven't found a proximate cause.

The *first* error has scrolled off the screen, but what I can see
an infinite stream (at about 20s intervals) of:

BUG: soft lockup - CPU#0 stuck for 22s! [kswapd0:317]
Pid: 317, comm: kswapd0 Not tainted 3.7.0-RC6 #224 HP Pavilion 04 P6319A-ABA 750N/P4B266LA
EIP: 0060:[<c10571f7>] EFLAGS: 00000202 CPU: 0
EIP is at __zone_watermark_ok+0x5f/7e, 0x67/7e, 0x6e/0x7e, or 0x74/7e
(Didn't type registers & stack)
Call Trace:
 [<c105774f>] ? zone_watermark_ok_safe+0x34/0x3a
 [<c105ec7e>] ? kswapd+0x2fa/0x6f6
 [<c105e984>] ? try_to_free_pages+0x4b8/0x4b8
 [<c103106b>] ? kthread+0x67/0x6c
 [<c12559b7>] ? ret_from_kernel_thread+0x1b/0x28
 [<c1031004>] ? -_kthread_parkme+0x4c.0x4c
Code: (didn't type in first line)
                                5f                        67                     6e                  74                             7e
 c9 39 d6 7f 14 eb 1c 6b c1 2c <8b> 44 05 60 d3 e0 29 c6 <d1> fb 39 de 7e 09 41 <39> f9 7c ea b0 01 <eb> 02 31 c0 5a 5b 5e 5f 5d c3 01 14 85 7c 16


The lack of scrollback limits me to 49 lines of SysRq output, and usually the most interesting
part disappears off the screen.  Two things I can see:

- SysRq-W shows no blocked tasks
- SysRq-M shows zero swap in use, and apparently adequate free memory
	DMA: <various segments> = 9048kB
	Normal: <various> = 116312kB
	HighMem: <various> = 41660kB
	416557 total pagecache pages
	0 pages in swap cache
	Swap cache stats: add 0, delete 0, find 0/0
	Free swap  = 4883724kB
	Total swap = 4883724kB
	524260 pages RAM
	296958 pages HighMem
	5221 pages reserved
	406417 pages shared
	351419 pages non-shared

Does anyone have any debugging suggestions?  Waiting overnight to
make a good/bad decision makes bisecting pretty slow...