------------[ cut here ]------------
WARNING: at /build/buildd/linux-2.6.28/drivers/usb/serial/usb-serial.c:313 serial_write+0x9f/0xb0()
Modules linked in: usb_storage ppp_deflate zlib_deflate bsd_comp ppp_async crc_ccitt i915 drm binfmt_misc bridge stp bnep input_polldev i8k sbp2 lp parport arc4 ecb joydev snd_hda_intel snd_pcm_oss snd_mixer_oss iwl3945 snd_pcm mac80211 led_class snd_timer snd soundcore intel_agp agpgart iTCO_wdt iTCO_vendor_support option cfg80211 snd_page_alloc video sdhci_pci sdhci psmouse dcdbas output pcspkr serio_raw sha256_generic aes_i586 aes_generic cbc ohci1394 ieee1394 b44 ssb mii dm_crypt fbcon tileblit font bitblit softcursor
Pid: 4, comm: ksoftirqd/0 Tainted: G        W  2.6.28-11-generic #38-Ubuntu
Call Trace:
 [<c0500e56>] ? printk+0x18/0x1a
 [<c0139b24>] warn_on_slowpath+0x54/0x80
 [<c0132168>] ? enqueue_task_fair+0x68/0x70
 [<c01287a7>] ? enqueue_task+0x57/0x70
 [<c0133b74>] ? try_to_wake_up+0x104/0x290
 [<c0127c8d>] ? update_curr+0x8d/0x1e0
 [<c03d688f>] serial_write+0x9f/0xb0
 [<f83f3c6b>] ppp_async_push+0xeb/0x130 [ppp_async]
 [<f83f42fd>] ppp_async_process+0x6d/0x80 [ppp_async]
 [<c013ed18>] tasklet_action+0x78/0x100
 [<c013f197>] __do_softirq+0x97/0x170
 [<c013f2cd>] do_softirq+0x5d/0x60
 [<c013f35a>] ksoftirqd+0x8a/0x120
 [<c013f2d0>] ? ksoftirqd+0x0/0x120
 [<c014e90c>] kthread+0x3c/0x70
 [<c014e8d0>] ? kthread+0x0/0x70
 [<c0105477>] kernel_thread_helper+0x7/0x10
---[ end trace f82dbcd00cb2fb8e ]---