I/O issues with writing to mtdblock devices on kirkwood

[andrew@lunn.ch (Andrew Lunn)]

On Mon, Jan 11, 2016 at 11:22:31PM +0000, Mark Brown wrote:
> On Mon, Jan 11, 2016 at 03:00:59PM -0800, Martin Michlmayr wrote:
> > A few months ago Debian users with QNAP devices (ARM Kirkwood)
> > reported issues (mostly SATA timeouts) when doing kernel upgrades,
> > specifically when the new ramdisk was being written to flash.
> 
> > cat file > /dev/mtdblockX worked fine on a 2 MB flash partition but
> > resulted in SATA timeouts on a 9 MB flash partition.
> 
> > flascp file /dev/mtd2 works fine.
> 
> > I've now bisected it down to this change:
> 
> >  commit 0461a4149836c792d186027c8c859637a4cfb11a
> >  Author: Mark Brown <broonie@kernel.org>
> >  Date:   Tue Dec 9 21:38:05 2014 +0000
> 
> >      spi: Pump transfers inside calling context for spi_sync()
> 
> Can you please clarify?  You're saying this causes SATA timeouts but
> this is a change in the SPI subsystem and you're talking about MTD
> devices.  You've also not said which kernel version this is with...

Hi Mark

I've done a little testing. What appears to happen is that while the
cat file > /dev/mtdblockX is going on, all access to filesystems on
SATA are blocked. I set off a "find ." and it busily prints
filenames. But as soon as i start the cat, it grinds to a halt, and
only continues once the cat has finished.

My guess is that the locking behaviour has changed somehow. SPI or MTD
is now holding onto a lock so preventing other filesystems making
progress? Maybe before this change the lock was release and grabbed every
message?

   Andrew