RE: Is it possible to corrupt disk when writeback page with undetected UE?

["Luck, Tony" <tony.luck@intel.com>]

> Were you using madvise to inject an error to a mmap'ed address?
> or a different tool?  Do you still have the test documented
> somewhere?

I was injecting with ACPI/EINJ (so tweaking some ECC bits in memory to create
a real uncorrectable error). This was a long time back when I was just trying to
get basic recovery from usermode access to poison working reliably. So I just
noted the workaround ("make; sync; run_test") to keep making progress.

Handling poison in the page cache has been on my TODO list for a long time.
Someday it will make it to the top.

> And, aside from verifying every write with a read prior to sync,
> any suggestion to minimize the window of such corruption?

There's no cheap solution. As you point out the best that can be done
is to reduce the window (since bits may get flipped after you perform
your check but before DMS to storage).

-Tony