crash in mmc subsystem during suspend

[Daniel Drake <dsd@laptop.org>]

Hi,

We're busy testing the suspend/resume functionality on the new OLPC
XO-1.5 laptop. This uses a SD card as its primary disk, which is on a
SDHCI controller on the VIA VX855 chipset. We are running Linux v2.6.31

We are occasionally encountering a crash from below mmc_rescan() during
suspend:

BUG: unable to handle kernel paging request at 6b6b6c57          
IP: [<b066d6e2>] sdio_remove_func+0x9/0x27
Call Trace:
[<b066cfb4>] ? mmc_sdio_remove+0x34/0x65                        
[<b066d1fc>] ? mmc_attach_sdio+0x217/0x240                      
[<b066a22f>] ? mmc_rescan+0x1a2/0x20f                           
[<b042e9a0>] ? worker_thread+0x156/0x1e1


This needs at least a few hundred suspend/resume cycles before it
reproduces, and often more than 2000.

Here is a log of the final couple of suspend/resumes and the crash:
http://dev.laptop.org/attachment/ticket/9707/p1_crash.log

and some of our diagnosis/discussion so far:
http://dev.laptop.org/ticket/9707

Does anyone have any theories on why this is happening?

Thanks,
Daniel