Every time I suspend or resume my laptop (Dell Latitude E6520, bought this year), I get 2 messages of the form displayed on the console just before shutting down/starting up:

[  407.107610] ehci_hcd 0000:00:1d.0: dma_pool_free buffer-128, f6f18000/36f18000 (bad dma)

On occasion, I get a message of the form:

[ 3753.979066] do_IRQ: 0.177 No irq handler for vector (irq -1)

On occasion, my machine freezes with a flashing Caps Lock button when suspending, after which I need to do a hard shutdown. This never happened before the messages started appearing (a while back), and I think it never happens without a do_IRQ message appearing (although I'm not sure about that). [There's nothing in the owner's manual on a flashing Caps Lock button; apparently it may be a kernel panic if the scroll lock also flashes, but the laptop doesn't have a scroll lock light, and there's no message on the console saying kernel panic.]

Are these bad DMA/do IRQ messages serious, and what can I do to investigate/troubleshoot them and the freezing?

Edit: I've also now received the following error messages a few times:

[246943.023908] JBD: I/O error detected when updating journal superblock for sdb1.
[246943.023958] Buffer I/O error on device sdb1, logical block 0
[246943.023996] EXT3-fs (sdb1): I/O error while writing superblock

Edit: Output of dmesg at http://pastebin.com/ra7MTQEj ; contents of /var/log/kern.log at http://pastebin.com/i6jf0Md9

Edit: the output of some smartctl (-a, -x, --log=error, --log=xerror) instructions is available at http://paste.ubuntu.com/1088488/ .

Edit (31/8/2012): Output of dmesg|grep -i ehci available at http://paste.ubuntu.com/1177246/ .