Re: scsi: myrs: warning fix, was: [GIT PULL] first round of SCSI updates for the 4.19+ merge window

From: Hannes Reinecke
Date: Fri Oct 26 2018 - 10:28:28 EST

On 10/26/18 10:16 AM, Arnd Bergmann wrote:
On Wed, Oct 24, 2018 at 1:00 PM James Bottomley
<James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:

James Bottomley (1):
scsi: myrs: fix build failure on 32 bit

Hi James and Hannes,

Since James mentioned 32-bit compiles during the kernel summit,
I'd like to confirm that I hit this on my randconfig builder now,
with some latency since the last linux-next tree I tested before
flying to Edinburgh did not have the bug, and the latest
linux-next tree that is available now (dated last Friday) does, and
I see your tree is fixed. During normal times, I should catch these
within a short time of the patch getting into scsi-next.

However, while looking at this bug, I found two more issues related
to the specific computation:

percent_complete = ldev_info->rbld_lba * 100 / ldev_info->cfg_devsize;

I see that both rbld_lba and cfg_devsize are reported by the
device, but only the former is 64 bit but the latter is 32 bit and
also intended to be the larger of the two. I suspect this is a
bug, and the same is also present in the old DAC960.c.
cfg_devsize is followed by four reserved bytes in the header,
so I suppose it was meant to be 64-bit?
If you divide two 64-bit numbers, you also have to use div_u64_64()
instead of do_div().

On top of that, I see we get those values from the device but
never do any endianess conversion on them. It seems likely
that they are all little-endian and require a le32_to_cpu()
conversion to also work on big-endian kernel builds. Alternatively
we could make the Kconfig symbol as

It _really_ is questionable if these device ever work on big-endian machines, as they rely on the BIOS to start up the RAID engine; I've had a hard enough time getting them to work on normal machines :-)

Plus the firmware refused to handle any drive larger than 4GB (!), so it's really a purely theoretical issue whether 'cfgsize' was meant to be 64 bit ...



Dr. Hannes Reinecke zSeries & Storage
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